Uploaded byveneethmathew
PPT, PDF10,034 views

Ch 14: Mendel and the Gene Idea

1) The document summarizes a chapter from a biology textbook about Gregor Mendel and his experiments with pea plants that established the basic principles of heredity and genetics. 2) Mendel conducted controlled crosses of pea plants with distinct, heritable traits and found that traits were passed to offspring in predictable ratios, such as a 3:1 ratio for some traits. 3) Mendel's work established the laws of segregation and independent assortment, which showed that traits are inherited as discrete units (now known as genes) that segregate and assort independently during reproduction.

Downloaded 395 times
1 / 108
2 / 108
3 / 108
4 / 108
5 / 108
6 / 108
7 / 108
8 / 108
9 / 108
10 / 108
11 / 108
12 / 108
13 / 108
14 / 108
15 / 108
16 / 108
17 / 108
18 / 108
19 / 108
20 / 108
21 / 108
22 / 108
23 / 108
24 / 108
25 / 108
26 / 108
27 / 108
28 / 108
29 / 108
30 / 108
31 / 108
32 / 108
33 / 108
Most read
34 / 108
35 / 108
36 / 108
37 / 108
38 / 108
39 / 108
Most read
40 / 108
Most read
41 / 108
42 / 108
43 / 108
44 / 108
45 / 108
46 / 108
47 / 108
48 / 108
49 / 108
50 / 108
51 / 108
52 / 108
53 / 108
54 / 108
55 / 108
56 / 108
57 / 108
58 / 108
59 / 108
60 / 108
61 / 108
62 / 108
63 / 108
64 / 108
65 / 108
66 / 108
67 / 108
68 / 108
69 / 108
70 / 108
71 / 108
72 / 108
73 / 108
74 / 108
75 / 108
76 / 108
77 / 108
78 / 108
79 / 108
80 / 108
81 / 108
82 / 108
83 / 108
84 / 108
85 / 108
86 / 108
87 / 108
88 / 108
89 / 108
90 / 108
91 / 108
92 / 108
93 / 108
94 / 108
95 / 108
96 / 108
97 / 108
98 / 108
99 / 108
100 / 108
101 / 108
102 / 108
103 / 108
104 / 108
105 / 108
106 / 108
107 / 108
108 / 108
LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson © 2011 Pearson Education, Inc. Lectures by Erin Barley Kathleen Fitzpatrick Mendel and the Gene Idea Chapter 14
Overview: Drawing from the Deck of Genes • What genetic principles account for the passing of traits from parents to offspring? • The “blending” hypothesis is the idea that genetic material from the two parents blends together (like blue and yellow paint blend to make green) © 2011 Pearson Education, Inc.
• The “particulate” hypothesis is the idea that parents pass on discrete heritable units (genes) • This hypothesis can explain the reappearance of traits after several generations • Mendel documented a particulate mechanism through his experiments with garden peas © 2011 Pearson Education, Inc.
Figure 14.1
Concept 14.1: Mendel used the scientific approach to identify two laws of inheritance • Mendel discovered the basic principles of heredity by breeding garden peas in carefully planned experiments © 2011 Pearson Education, Inc.
Mendel’s Experimental, Quantitative Approach • Advantages of pea plants for genetic study – There are many varieties with distinct heritable features, or characters (such as flower color); character variants (such as purple or white flowers) are called traits – Mating can be controlled – Each flower has sperm-producing organs (stamens) and an egg-producing organ (carpel) – Cross-pollination (fertilization between different plants) involves dusting one plant with pollen from another © 2011 Pearson Education, Inc.
Figure 14.2 Parental generation (P) Stamens Carpel First filial generation offspring (F1) TECHNIQUE RESULTS 3 2 1 4 5
Figure 14.2a Parental generation (P) Stamens Carpel TECHNIQUE 2 1 3 4
Figure 14.2b First filial generation offspring (F1) RESULTS 5
• Mendel chose to track only those characters that occurred in two distinct alternative forms • He also used varieties that were true-breeding (plants that produce offspring of the same variety when they self-pollinate) © 2011 Pearson Education, Inc.
• In a typical experiment, Mendel mated two contrasting, true-breeding varieties, a process called hybridization • The true-breeding parents are the P generation • The hybrid offspring of the P generation are called the F1 generation • When F1 individuals self-pollinate or cross- pollinate with other F1 hybrids, the F2 generation is produced © 2011 Pearson Education, Inc.
The Law of Segregation • When Mendel crossed contrasting, true- breeding white- and purple-flowered pea plants, all of the F1 hybrids were purple • When Mendel crossed the F1 hybrids, many of the F2 plants had purple flowers, but some had white • Mendel discovered a ratio of about three to one, purple to white flowers, in the F2 generation © 2011 Pearson Education, Inc.
Figure 14.3-1 P Generation EXPERIMENT (true-breeding parents) Purple flowers White flowers
Figure 14.3-2 P Generation EXPERIMENT (true-breeding parents) F1 Generation (hybrids) Purple flowers White flowers All plants had purple flowers Self- or cross-pollination
Figure 14.3-3 P Generation EXPERIMENT (true-breeding parents) F1 Generation (hybrids) F2 Generation Purple flowers White flowers All plants had purple flowers Self- or cross-pollination 705 purple- flowered plants 224 white flowered plants
• Mendel reasoned that only the purple flower factor was affecting flower color in the F1 hybrids • Mendel called the purple flower color a dominant trait and the white flower color a recessive trait • The factor for white flowers was not diluted or destroyed because it reappeared in the F2 generation © 2011 Pearson Education, Inc.
• Mendel observed the same pattern of inheritance in six other pea plant characters, each represented by two traits • What Mendel called a “heritable factor” is what we now call a gene © 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.
Table 14.1
Mendel’s Model • Mendel developed a hypothesis to explain the 3:1 inheritance pattern he observed in F2 offspring • Four related concepts make up this model • These concepts can be related to what we now know about genes and chromosomes © 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.
• First: alternative versions of genes account for variations in inherited characters • For example, the gene for flower color in pea plants exists in two versions, one for purple flowers and the other for white flowers • These alternative versions of a gene are now called alleles • Each gene resides at a specific locus on a specific chromosome © 2011 Pearson Education, Inc.
Figure 14.4 Allele for purple flowers Locus for flower-color gene Allele for white flowers Pair of homologous chromosomes
• Second: for each character, an organism inherits two alleles, one from each parent • Mendel made this deduction without knowing about the role of chromosomes • The two alleles at a particular locus may be identical, as in the true-breeding plants of Mendel’s P generation • Alternatively, the two alleles at a locus may differ, as in the F1 hybrids © 2011 Pearson Education, Inc.
• Third: if the two alleles at a locus differ, then one (the dominant allele) determines the organism’s appearance, and the other (the recessive allele) has no noticeable effect on appearance • In the flower-color example, the F1 plants had purple flowers because the allele for that trait is dominant © 2011 Pearson Education, Inc.
• Fourth (now known as the law of segregation): the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes • Thus, an egg or a sperm gets only one of the two alleles that are present in the organism • This segregation of alleles corresponds to the distribution of homologous chromosomes to different gametes in meiosis © 2011 Pearson Education, Inc.
• Mendel’s segregation model accounts for the 3:1 ratio he observed in the F2 generation of his numerous crosses • The possible combinations of sperm and egg can be shown using a Punnett square, a diagram for predicting the results of a genetic cross between individuals of known genetic makeup • A capital letter represents a dominant allele, and a lowercase letter represents a recessive allele © 2011 Pearson Education, Inc.
Figure 14.5-1 P Generation Appearance: Genetic makeup: Gametes: Purple flowers White flowers PP pp P p
Figure 14.5-2 P Generation F1 Generation Appearance: Genetic makeup: Gametes: Appearance: Genetic makeup: Gametes: Purple flowers White flowers Purple flowers Pp PP pp P P p p1 /2 1 /2
Figure 14.5-3 P Generation F1 Generation F2 Generation Appearance: Genetic makeup: Gametes: Appearance: Genetic makeup: Gametes: Purple flowers White flowers Purple flowers Sperm from F1 (Pp) plant Pp PP pp P P P P p p p p Eggs from F1 (Pp) plant PP ppPp Pp 1 /2 1 /2 3 : 1
Useful Genetic Vocabulary • An organism with two identical alleles for a character is said to be homozygous for the gene controlling that character • An organism that has two different alleles for a gene is said to be heterozygous for the gene controlling that character • Unlike homozygotes, heterozygotes are not true-breeding © 2011 Pearson Education, Inc.
• Because of the different effects of dominant and recessive alleles, an organism’s traits do not always reveal its genetic composition • Therefore, we distinguish between an organism’s phenotype, or physical appearance, and its genotype, or genetic makeup • In the example of flower color in pea plants, PP and Pp plants have the same phenotype (purple) but different genotypes © 2011 Pearson Education, Inc.
Phenotype Purple Purple Purple White 3 1 1 1 2 Ratio 3:1 Ratio 1:2:1 Genotype PP (homozygous) Pp (heterozygous) Pp (heterozygous) pp (homozygous) Figure 14.6
The Testcross • How can we tell the genotype of an individual with the dominant phenotype? • Such an individual could be either homozygous dominant or heterozygous • The answer is to carry out a testcross: breeding the mystery individual with a homozygous recessive individual • If any offspring display the recessive phenotype, the mystery parent must be heterozygous © 2011 Pearson Education, Inc.
Figure 14.7 Dominant phenotype, unknown genotype: PP or Pp? Recessive phenotype, known genotype: pp Predictions If purple-flowered parent is PP If purple-flowered parent is Pp or Sperm Sperm Eggs Eggs or All offspring purple 1 /2 offspring purple and 1 /2 offspring white Pp Pp Pp Pp Pp Pp pp pp p p p p P P P p TECHNIQUE RESULTS
The Law of Independent Assortment • Mendel derived the law of segregation by following a single character • The F1 offspring produced in this cross were monohybrids, individuals that are heterozygous for one character • A cross between such heterozygotes is called a monohybrid cross © 2011 Pearson Education, Inc.
• Mendel identified his second law of inheritance by following two characters at the same time • Crossing two true-breeding parents differing in two characters produces dihybrids in the F1 generation, heterozygous for both characters • A dihybrid cross, a cross between F1 dihybrids, can determine whether two characters are transmitted to offspring as a package or independently © 2011 Pearson Education, Inc.
Figure 14.8 P Generation F1 Generation Predictions Gametes EXPERIMENT RESULTS YYRR yyrr yrYR YyRr Hypothesis of dependent assortment Hypothesis of independent assortment Predicted offspring of F2 generation Sperm Sperm or Eggs Eggs Phenotypic ratio 3:1 Phenotypic ratio 9:3:3:1 Phenotypic ratio approximately 9:3:3:1315 108 101 32 1 /2 1 /2 1 /2 1 /2 1 /4 1 /4 1 /4 1 /4 1 /4 1 /4 1 /4 1 /4 9 /16 3 /16 3 /16 1 /16 YR YR YR YR yr yr yr yr 1 /4 3 /4 Yr Yr yR yR YYRR YyRr YyRr yyrr YYRR YYRr YyRR YyRr YYRr YYrr YyRr Yyrr YyRR YyRr yyRR yyRr YyRr Yyrr yyRr yyrr
• Using a dihybrid cross, Mendel developed the law of independent assortment • The law of independent assortment states that each pair of alleles segregates independently of each other pair of alleles during gamete formation • Strictly speaking, this law applies only to genes on different, nonhomologous chromosomes or those far apart on the same chromosome • Genes located near each other on the same chromosome tend to be inherited together © 2011 Pearson Education, Inc.
Concept 14.2: The laws of probability govern Mendelian inheritance • Mendel’s laws of segregation and independent assortment reflect the rules of probability • When tossing a coin, the outcome of one toss has no impact on the outcome of the next toss • In the same way, the alleles of one gene segregate into gametes independently of another gene’s alleles © 2011 Pearson Education, Inc.
• The multiplication rule states that the probability that two or more independent events will occur together is the product of their individual probabilities • Probability in an F1 monohybrid cross can be determined using the multiplication rule • Segregation in a heterozygous plant is like flipping a coin: Each gamete has a chance of carrying the dominant allele and a chance of carrying the recessive allele The Multiplication and Addition Rules Applied to Monohybrid Crosses 1 2 1 2 © 2011 Pearson Education, Inc.
Figure 14.9 Segregation of alleles into eggs Segregation of alleles into sperm Sperm Eggs 1 /2 1 /2 1 /2 1 /2 1 /4 1 /4 1 /4 1 /4 Rr Rr R R R R R R r r r r r × r
• The addition rule states that the probability that any one of two or more exclusive events will occur is calculated by adding together their individual probabilities • The rule of addition can be used to figure out the probability that an F2 plant from a monohybrid cross will be heterozygous rather than homozygous © 2011 Pearson Education, Inc.
Solving Complex Genetics Problems with the Rules of Probability • We can apply the multiplication and addition rules to predict the outcome of crosses involving multiple characters • A dihybrid or other multicharacter cross is equivalent to two or more independent monohybrid crosses occurring simultaneously • In calculating the chances for various genotypes, each character is considered separately, and then the individual probabilities are multiplied © 2011 Pearson Education, Inc.
Figure 14.UN01 Probability of YYRR Probability of YyRR 1 /4 (probability of YY) 1 /2 (Yy) 1 /4 (RR) 1 /4 (RR) 1 /16 1 /8 = × ×= = =
Figure 14.UN02 Chance of at least two recessive traits ppyyRr ppYyrr Ppyyrr PPyyrr ppyyrr 1 /4 (probability of pp) × 1 /2 (yy) × 1 /2 (Rr) 1 /4 × 1 /2 × 1 /2 1 /2 × 1 /2 × 1 /2 1 /4 × 1 /2 × 1 /2 1 /4 × 1 /2 × 1 /2 = 1 /16 = 1 /16 = 2 /16 = 1 /16 = 1 /16 = 6 /16 or 3 /8
Concept 14.3: Inheritance patterns are often more complex than predicted by simple Mendelian genetics • The relationship between genotype and phenotype is rarely as simple as in the pea plant characters Mendel studied • Many heritable characters are not determined by only one gene with two alleles • However, the basic principles of segregation and independent assortment apply even to more complex patterns of inheritance © 2011 Pearson Education, Inc.
Extending Mendelian Genetics for a Single Gene • Inheritance of characters by a single gene may deviate from simple Mendelian patterns in the following situations: – When alleles are not completely dominant or recessive – When a gene has more than two alleles – When a gene produces multiple phenotypes © 2011 Pearson Education, Inc.
Degrees of Dominance • Complete dominance occurs when phenotypes of the heterozygote and dominant homozygote are identical • In incomplete dominance, the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties • In codominance, two dominant alleles affect the phenotype in separate, distinguishable ways © 2011 Pearson Education, Inc.
Figure 14.10-1 P Generation Red White Gametes CW CW CR CR CR CW
Figure 14.10-2 P Generation F1 Generation 1 /2 1 /2 Red White Gametes Pink Gametes CW CW CR CR CR CW CR CW CR CW
Figure 14.10-3 P Generation F1 Generation F2 Generation 1 /2 1 /2 1 /2 1 /2 1 /2 1 /2 Red White Gametes Pink Gametes Sperm Eggs CW CW CR CR CR CW CR CW CR CW CW CR CR CW CR CR CR CW CR CW CW CW
• A dominant allele does not subdue a recessive allele; alleles don’t interact that way • Alleles are simply variations in a gene’s nucleotide sequence • For any character, dominance/recessiveness relationships of alleles depend on the level at which we examine the phenotype The Relation Between Dominance and Phenotype © 2011 Pearson Education, Inc.
• Tay-Sachs disease is fatal; a dysfunctional enzyme causes an accumulation of lipids in the brain – At the organismal level, the allele is recessive – At the biochemical level, the phenotype (i.e., the enzyme activity level) is incompletely dominant – At the molecular level, the alleles are codominant © 2011 Pearson Education, Inc.
Frequency of Dominant Alleles • Dominant alleles are not necessarily more common in populations than recessive alleles • For example, one baby out of 400 in the United States is born with extra fingers or toes © 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.
• The allele for this unusual trait is dominant to the allele for the more common trait of five digits per appendage • In this example, the recessive allele is far more prevalent than the population’s dominant allele © 2011 Pearson Education, Inc.
Multiple Alleles • Most genes exist in populations in more than two allelic forms • For example, the four phenotypes of the ABO blood group in humans are determined by three alleles for the enzyme (I) that attaches A or B carbohydrates to red blood cells: IA , IB , and i. • The enzyme encoded by the IA allele adds the A carbohydrate, whereas the enzyme encoded by the IB allele adds the B carbohydrate; the enzyme encoded by the i allele adds neither © 2011 Pearson Education, Inc.
Figure 14.11 Carbohydrate Allele (a) The three alleles for the ABO blood groups and their carbohydrates (b) Blood group genotypes and phenotypes Genotype Red blood cell appearance Phenotype (blood group) A A B B AB none O IA IB i iiIA IBIA IA or IA i IB IB or IB i
Pleiotropy • Most genes have multiple phenotypic effects, a property called pleiotropy • For example, pleiotropic alleles are responsible for the multiple symptoms of certain hereditary diseases, such as cystic fibrosis and sickle-cell disease © 2011 Pearson Education, Inc.
Extending Mendelian Genetics for Two or More Genes • Some traits may be determined by two or more genes © 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.
Epistasis • In epistasis, a gene at one locus alters the phenotypic expression of a gene at a second locus • For example, in Labrador retrievers and many other mammals, coat color depends on two genes • One gene determines the pigment color (with alleles B for black and b for brown) • The other gene (with alleles C for color and c for no color) determines whether the pigment will be deposited in the hair © 2011 Pearson Education, Inc.
Figure 14.12 Sperm Eggs 9 : 3 : 4 1 /4 1 /4 1 /4 1 /4 1 /4 1 /4 1 /4 1 /4 BbEe BbEe BE BE bE bE Be Be be be BBEE BbEE BBEe BbEe BbEE bbEE BbEe bbEe BBEe BbEe BBee Bbee BbEe bbEe Bbee bbee
Polygenic Inheritance • Quantitative characters are those that vary in the population along a continuum • Quantitative variation usually indicates polygenic inheritance, an additive effect of two or more genes on a single phenotype • Skin color in humans is an example of polygenic inheritance © 2011 Pearson Education, Inc.
Figure 14.13 Eggs Sperm Phenotypes: Number of dark-skin alleles: 0 1 2 3 4 5 6 1 /8 1 /8 1 /8 1 /8 1 /8 1 /8 1 /8 1 /8 1 /8 1 /8 1 /8 1 /8 1 /8 1 /8 1 /8 1 /8 1 /64 6 /64 15 /64 20 /64 15 /64 6 /64 1 /64 AaBbCc AaBbCc
Nature and Nurture: The Environmental Impact on Phenotype • Another departure from Mendelian genetics arises when the phenotype for a character depends on environment as well as genotype • The norm of reaction is the phenotypic range of a genotype influenced by the environment • For example, hydrangea flowers of the same genotype range from blue-violet to pink, depending on soil acidity © 2011 Pearson Education, Inc.
Figure 14.14
Figure 14.14a
Figure 14.14b
• Norms of reaction are generally broadest for polygenic characters • Such characters are called multifactorial because genetic and environmental factors collectively influence phenotype © 2011 Pearson Education, Inc.
Integrating a Mendelian View of Heredity and Variation • An organism’s phenotype includes its physical appearance, internal anatomy, physiology, and behavior • An organism’s phenotype reflects its overall genotype and unique environmental history © 2011 Pearson Education, Inc.
Concept 14.4: Many human traits follow Mendelian patterns of inheritance • Humans are not good subjects for genetic research – Generation time is too long – Parents produce relatively few offspring – Breeding experiments are unacceptable • However, basic Mendelian genetics endures as the foundation of human genetics © 2011 Pearson Education, Inc.
Pedigree Analysis • A pedigree is a family tree that describes the interrelationships of parents and children across generations • Inheritance patterns of particular traits can be traced and described using pedigrees © 2011 Pearson Education, Inc.
Figure 14.15 Key Male Female Affected male Affected female Mating Offspring 1st generation 2nd generation 3rd generation 1st generation 2nd generation 3rd generation Is a widow’s peak a dominant or recessive trait? (a) Is an attached earlobe a dominant or recessive trait? b) Widow’s peak No widow’s peak Attached earlobe Free earlobe FF or FfWW or Ww Ww ww ww Ww Ww Ww Wwww ww ww ww Ff Ff Ff Ff Ff ff ffffffFF or Ff ff
Figure 14.15a Widow’s peak
Figure 14.15b No widow’s peak
Figure 14.15c Attached earlobe
Figure 14.15d Free earlobe
• Pedigrees can also be used to make predictions about future offspring • We can use the multiplication and addition rules to predict the probability of specific phenotypes © 2011 Pearson Education, Inc.
Recessively Inherited Disorders • Many genetic disorders are inherited in a recessive manner • These range from relatively mild to life- threatening © 2011 Pearson Education, Inc.
The Behavior of Recessive Alleles • Recessively inherited disorders show up only in individuals homozygous for the allele • Carriers are heterozygous individuals who carry the recessive allele but are phenotypically normal; most individuals with recessive disorders are born to carrier parents • Albinism is a recessive condition characterized by a lack of pigmentation in skin and hair © 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.
Figure 14.16 Parents Normal Aa Sperm Eggs Normal Aa AA Normal Aa Normal (carrier) Aa Normal (carrier) aa Albino A A a a
Figure 14.16a
• If a recessive allele that causes a disease is rare, then the chance of two carriers meeting and mating is low • Consanguineous matings (i.e., matings between close relatives) increase the chance of mating between two carriers of the same rare allele • Most societies and cultures have laws or taboos against marriages between close relatives © 2011 Pearson Education, Inc.
Cystic Fibrosis • Cystic fibrosis is the most common lethal genetic disease in the United States,striking one out of every 2,500 people of European descent • The cystic fibrosis allele results in defective or absent chloride transport channels in plasma membranes leading to a buildup of chloride ions outside the cell • Symptoms include mucus buildup in some internal organs and abnormal absorption of nutrients in the small intestine © 2011 Pearson Education, Inc.
Sickle-Cell Disease: A Genetic Disorder with Evolutionary Implications • Sickle-cell disease affects one out of 400 African-Americans • The disease is caused by the substitution of a single amino acid in the hemoglobin protein in red blood cells • In homozygous individuals, all hemoglobin is abnormal (sickle-cell) • Symptoms include physical weakness, pain, organ damage, and even paralysis © 2011 Pearson Education, Inc.
Fig. 14-UN1 © 2011 Pearson Education, Inc. • Heterozygotes (said to have sickle-cell trait) are usually healthy but may suffer some symptoms • About one out of ten African Americans has sickle cell trait, an unusually high frequency of an allele with detrimental effects in homozygotes • Heterozygotes are less susceptible to the malaria parasite, so there is an advantage to being heterozygous
Dominantly Inherited Disorders • Some human disorders are caused by dominant alleles • Dominant alleles that cause a lethal disease are rare and arise by mutation • Achondroplasia is a form of dwarfism caused by a rare dominant allele © 2011 Pearson Education, Inc.
Figure 14.17 Parents Dwarf Dd Sperm Eggs Dd Dwarf dd Normal Dd Dwarf dd Normal D d d d Normal dd
Figure 14.17a
• The timing of onset of a disease significantly affects its inheritance • Huntington’s disease is a degenerative disease of the nervous system • The disease has no obvious phenotypic effects until the individual is about 35 to 40 years of age • Once the deterioration of the nervous system begins the condition is irreversible and fatal Huntington’s Disease: A Late-Onset Lethal Disease © 2011 Pearson Education, Inc.
Multifactorial Disorders • Many diseases, such as heart disease, diabetes, alcoholism, mental illnesses, and cancer have both genetic and environmental components • Little is understood about the genetic contribution to most multifactorial diseases © 2011 Pearson Education, Inc.
Genetic Testing and Counseling • Genetic counselors can provide information to prospective parents concerned about a family history for a specific disease © 2011 Pearson Education, Inc.
Counseling Based on Mendelian Genetics and Probability Rules • Using family histories, genetic counselors help couples determine the odds that their children will have genetic disorders • Probabilities are predicted on the most accurate information at the time; predicted probabilities may change as new information is available © 2011 Pearson Education, Inc.
Tests for Identifying Carriers • For a growing number of diseases, tests are available that identify carriers and help define the odds more accurately © 2011 Pearson Education, Inc.
Figure 14.18
Fetal Testing • In amniocentesis, the liquid that bathes the fetus is removed and tested • In chorionic villus sampling (CVS), a sample of the placenta is removed and tested • Other techniques, such as ultrasound and fetoscopy, allow fetal health to be assessed visually in utero © 2011 Pearson Education, Inc. Video: Ultrasound of Human Fetus I
Figure 14.19 (a) Amniocentesis (b) Chorionic villus sampling (CVS) Ultrasound monitor Amniotic fluid withdrawn Fetus Placenta Uterus Cervix Centrifugation Fluid Fetal cells Several hours Several weeks Several weeks Biochemical and genetic tests Karyotyping Ultrasound monitor Fetus Placenta Chorionic villi Uterus Cervix Suction tube inserted through cervix Several hours Fetal cells Several hours 1 1 2 2 3
Newborn Screening • Some genetic disorders can be detected at birth by simple tests that are now routinely performed in most hospitals in the United States © 2011 Pearson Education, Inc.
Figure 14.UN03 Complete dominance of one allele Relationship among alleles of a single gene Description Example Incomplete dominance of either allele Codominance Multiple alleles Pleiotropy Heterozygous phenotype same as that of homo- zygous dominant Heterozygous phenotype intermediate between the two homozygous phenotypes Both phenotypes expressed in heterozygotes In the whole population, some genes have more than two alleles One gene is able to affect multiple phenotypic characters ABO blood group alleles Sickle-cell disease PP Pp CR CR CR CW CW CW IA IB IA , IB , i
Figure 14.UN04 Epistasis Polygenic inheritance Relationship among two or more genes Description Example The phenotypic expression of one gene affects that of another A single phenotypic character is affected by two or more genes 9 : 3 : 4 BbEe BbEe BE BE bE bE Be Be be be AaBbCc AaBbCc
Figure 14.UN05 Flower position Stem length Seed shape Character Dominant Recessive Axial (A) Tall (T) Round (R) Terminal (a) Dwarf (t) Wrinkled (r)
Figure 14.UN06
Figure 14.UN07 George Arlene Sandra Tom Sam Wilma Ann Michael Carla Daniel Alan Tina Christopher
Figure 14.UN08
Figure 14.UN09
Figure 14.UN10
Figure 14.UN11
Figure 14.UN12
Figure 14.UN13
Figure 14.UN14

More Related Content

PPT
Ch 15: The Chromosomal Basis of Inheritance
byveneethmathew
 
PPT
Ch 16: The Molecular Basis of Inheritance
byveneethmathew
 
PPT
21 lecture genome_and_evolution
byveneethmathew
 
PPT
Ch 13: Meiosis and Sexual Life Cycles
byveneethmathew
 
PPT
23 lecture evolution_populations
byveneethmathew
 
PPT
14 mendel and the gene idea
bykindarspirit
 
PPT
20 lecture biotech
byveneethmathew
 
PPT
22 lecture descent_with_modification
byveneethmathew
 
Ch 15: The Chromosomal Basis of Inheritance
byveneethmathew
 
Ch 16: The Molecular Basis of Inheritance
byveneethmathew
 
21 lecture genome_and_evolution
byveneethmathew
 
Ch 13: Meiosis and Sexual Life Cycles
byveneethmathew
 
23 lecture evolution_populations
byveneethmathew
 
14 mendel and the gene idea
bykindarspirit
 
20 lecture biotech
byveneethmathew
 
22 lecture descent_with_modification
byveneethmathew
 

What's hot

PPT
Ch 17: From Gene to Protein
byveneethmathew
 
PPT
16 the molecular basis of inheritance
bykindarspirit
 
PPT
18 Regulation of Gene Expression
bykindarspirit
 
PPT
17 - From Gene to Protein
bykindarspirit
 
PPT
26 lecture phylogeny
byveneethmathew
 
PPT
23 the evolution of populations
bykindarspirit
 
PPT
Ch 8: Introduction to Metabolism
byveneethmathew
 
PPT
12 the cell cycle
bykindarspirit
 
PPT
25 lecture history_of_life
byveneethmathew
 
PPT
Ch 12: Cell Cycle
byveneethmathew
 
PPT
13 meiosis and sexual life cycles
bykindarspirit
 
PPT
Ch 7: Membrane Structure and Function
byveneethmathew
 
PPT
21 genomes and their evolution
bykindarspirit
 
PPT
19 - Viruses
bykindarspirit
 
PPT
24 lecture origin_of_species
byveneethmathew
 
PPT
22 descent with modification a darwinian view
bykindarspirit
 
PPT
27 lecture bacteria
byveneethmathew
 
PPT
Chapter52
byuv5
 
PPT
Ch 11: Cell Communication
byveneethmathew
 
PPT
Biology in Focus - Chapter 18
bympattani
 
Ch 17: From Gene to Protein
byveneethmathew
 
16 the molecular basis of inheritance
bykindarspirit
 
18 Regulation of Gene Expression
bykindarspirit
 
17 - From Gene to Protein
bykindarspirit
 
26 lecture phylogeny
byveneethmathew
 
23 the evolution of populations
bykindarspirit
 
Ch 8: Introduction to Metabolism
byveneethmathew
 
12 the cell cycle
bykindarspirit
 
25 lecture history_of_life
byveneethmathew
 
Ch 12: Cell Cycle
byveneethmathew
 
13 meiosis and sexual life cycles
bykindarspirit
 
Ch 7: Membrane Structure and Function
byveneethmathew
 
21 genomes and their evolution
bykindarspirit
 
19 - Viruses
bykindarspirit
 
24 lecture origin_of_species
byveneethmathew
 
22 descent with modification a darwinian view
bykindarspirit
 
27 lecture bacteria
byveneethmathew
 
Chapter52
byuv5
 
Ch 11: Cell Communication
byveneethmathew
 
Biology in Focus - Chapter 18
bympattani
 

Similar to Ch 14: Mendel and the Gene Idea

PPT
14 lecture presentation revised
byJill Creswell
 
PPT
14 lecture presentation
by1slid
 
PPT
14mendelandthegeneidea 130311053443-phpapp01
byCleophas Rwemera
 
PPTX
14 ge lecture presentation
bymahmood jassim
 
PPTX
14 lecture BIOL 1010-30 Gillette College
bydeskam2
 
PDF
Harakamaljit
byHarKamal2
 
PDF
Genetics mendelian.ppt
byJasper Obico
 
PPT
chapter14_mendel_and_gene_idea poulami.ppt
byPoulamiMukherjee41
 
PPT
Biology in Focus - Chapter 11
bympattani
 
PPT
11lecturepresentation 151117172044-lva1-app6891
byCleophas Rwemera
 
PPT
14 mendel text
byAndrew McCaskill
 
PPT
Ch5 linkage
byPratheep Sandrasaigaran
 
PPT
Chapter14genes 151125145851-lva1-app6891
byCleophas Rwemera
 
PPT
Chapter 14: Mendel and Genes
byAngel Vega
 
PPT
Chapter14genes 151125145851-lva1-app6891
byCleophas Rwemera
 
PDF
Mendelian genetics lecture quiz
byMarilen Parungao
 
PPT
14 A Grgor Mendals Discovries
bysreed
 
PPTX
GenBio2 - Lesson 1 - Introduction to Genetics.pptx
byBerniceCayabyab1
 
PPT
Biology: All about Genetics
byPadme Amidala
 
PPTX
General-Biology----------2_Genetics.pptx
byetonblue
 
14 lecture presentation revised
byJill Creswell
 
14 lecture presentation
by1slid
 
14mendelandthegeneidea 130311053443-phpapp01
byCleophas Rwemera
 
14 ge lecture presentation
bymahmood jassim
 
14 lecture BIOL 1010-30 Gillette College
bydeskam2
 
Harakamaljit
byHarKamal2
 
Genetics mendelian.ppt
byJasper Obico
 
chapter14_mendel_and_gene_idea poulami.ppt
byPoulamiMukherjee41
 
Biology in Focus - Chapter 11
bympattani
 
11lecturepresentation 151117172044-lva1-app6891
byCleophas Rwemera
 
14 mendel text
byAndrew McCaskill
 
Ch5 linkage
byPratheep Sandrasaigaran
 
Chapter14genes 151125145851-lva1-app6891
byCleophas Rwemera
 
Chapter 14: Mendel and Genes
byAngel Vega
 
Chapter14genes 151125145851-lva1-app6891
byCleophas Rwemera
 
Mendelian genetics lecture quiz
byMarilen Parungao
 
14 A Grgor Mendals Discovries
bysreed
 
GenBio2 - Lesson 1 - Introduction to Genetics.pptx
byBerniceCayabyab1
 
Biology: All about Genetics
byPadme Amidala
 
General-Biology----------2_Genetics.pptx
byetonblue
 

More from veneethmathew

PPT
19 lecture viruses
byveneethmathew
 
PPT
Ch 10: Photosynthesis
byveneethmathew
 
PPT
Ch 9: Cell Respiration and Fermentation
byveneethmathew
 
PPT
Ch 6: A Tour of the Cell
byveneethmathew
 
PPT
Ch 5: The Structure and Function of Large Biological Molecules
byveneethmathew
 
PPT
Ch 4: Carbon and Diversity
byveneethmathew
 
PPT
Ch 3: Water and Life
byveneethmathew
 
PPT
Ch 2: The Chemical Context of Life
byveneethmathew
 
PPT
Ch 1: Themes in the Study of Life
byveneethmathew
 
19 lecture viruses
byveneethmathew
 
Ch 10: Photosynthesis
byveneethmathew
 
Ch 9: Cell Respiration and Fermentation
byveneethmathew
 
Ch 6: A Tour of the Cell
byveneethmathew
 
Ch 5: The Structure and Function of Large Biological Molecules
byveneethmathew
 
Ch 4: Carbon and Diversity
byveneethmathew
 
Ch 3: Water and Life
byveneethmathew
 
Ch 2: The Chemical Context of Life
byveneethmathew
 
Ch 1: Themes in the Study of Life
byveneethmathew
 
In this document
Powered by AI

Lecture on 'Mendel and the Gene Idea' from Campbell Biology, ninth edition.

Overview of blending vs. particulate hypotheses; Mendel's experiments with pea plants.

Mendel's methods: controlled mating of true-breeding pea plants leading to identification of traits.

Mendel's findings on flower color inheritance; 3:1 ratio of purple to white flowers in F2 generation.

Mendel's hypothesis relating genes, alleles, and chromosomes; law of segregation.

Use of Punnett squares for predicting genetic cross outcomes and understanding genotypes.

Mendel’s second law: two characters’ alleles segregate independently in dihybrid crosses.

Application of Mendel's laws through rules of probability; multiplication and addition rules.

Discussion on complex genetic inheritance patterns beyond simple Mendelian genetics.

Exploration of alleles' variability in traits and the pleiotropic effects of genes.

Interactions between multiple genes affecting phenotypes; examples including skin color.

Role of environmental factors alongside genetics in determining phenotypes.

Challenges of studying human genetics and using pedigrees for trait inheritance analysis.

Overview of recessively inherited disorders, examples like Albinism and carrier concepts.

Analysis of cystic fibrosis and sickle-cell disease, their prevalence, and implications. Characteristics of dominantly inherited disorders, including Huntington’s disease.

Role of genetic counselors in assessing risks and using tests for genetic disorders.

Routine tests for genetic disorders performed at birth in hospitals.

Recap of genetic dominance, alleles, inheritance relationships, and examples.

Examples of genetic traits analysis through family trees and inheritance patterns.

Ch 14: Mendel and the Gene Idea

  • 1.
    LECTURE PRESENTATIONS For CAMPBELLBIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson © 2011 Pearson Education, Inc. Lectures by Erin Barley Kathleen Fitzpatrick Mendel and the Gene Idea Chapter 14
  • 2.
    Overview: Drawing fromthe Deck of Genes • What genetic principles account for the passing of traits from parents to offspring? • The “blending” hypothesis is the idea that genetic material from the two parents blends together (like blue and yellow paint blend to make green) © 2011 Pearson Education, Inc.
  • 3.
    • The “particulate”hypothesis is the idea that parents pass on discrete heritable units (genes) • This hypothesis can explain the reappearance of traits after several generations • Mendel documented a particulate mechanism through his experiments with garden peas © 2011 Pearson Education, Inc.
  • 4.
  • 5.
    Concept 14.1: Mendelused the scientific approach to identify two laws of inheritance • Mendel discovered the basic principles of heredity by breeding garden peas in carefully planned experiments © 2011 Pearson Education, Inc.
  • 6.
    Mendel’s Experimental, Quantitative Approach •Advantages of pea plants for genetic study – There are many varieties with distinct heritable features, or characters (such as flower color); character variants (such as purple or white flowers) are called traits – Mating can be controlled – Each flower has sperm-producing organs (stamens) and an egg-producing organ (carpel) – Cross-pollination (fertilization between different plants) involves dusting one plant with pollen from another © 2011 Pearson Education, Inc.
  • 7.
  • 8.
  • 9.
  • 10.
    • Mendel choseto track only those characters that occurred in two distinct alternative forms • He also used varieties that were true-breeding (plants that produce offspring of the same variety when they self-pollinate) © 2011 Pearson Education, Inc.
  • 11.
    • In atypical experiment, Mendel mated two contrasting, true-breeding varieties, a process called hybridization • The true-breeding parents are the P generation • The hybrid offspring of the P generation are called the F1 generation • When F1 individuals self-pollinate or cross- pollinate with other F1 hybrids, the F2 generation is produced © 2011 Pearson Education, Inc.
  • 12.
    The Law ofSegregation • When Mendel crossed contrasting, true- breeding white- and purple-flowered pea plants, all of the F1 hybrids were purple • When Mendel crossed the F1 hybrids, many of the F2 plants had purple flowers, but some had white • Mendel discovered a ratio of about three to one, purple to white flowers, in the F2 generation © 2011 Pearson Education, Inc.
  • 13.
  • 14.
    Figure 14.3-2 P Generation EXPERIMENT (true-breeding parents) F1Generation (hybrids) Purple flowers White flowers All plants had purple flowers Self- or cross-pollination
  • 15.
    Figure 14.3-3 P Generation EXPERIMENT (true-breeding parents) F1Generation (hybrids) F2 Generation Purple flowers White flowers All plants had purple flowers Self- or cross-pollination 705 purple- flowered plants 224 white flowered plants
  • 16.
    • Mendel reasonedthat only the purple flower factor was affecting flower color in the F1 hybrids • Mendel called the purple flower color a dominant trait and the white flower color a recessive trait • The factor for white flowers was not diluted or destroyed because it reappeared in the F2 generation © 2011 Pearson Education, Inc.
  • 17.
    • Mendel observedthe same pattern of inheritance in six other pea plant characters, each represented by two traits • What Mendel called a “heritable factor” is what we now call a gene © 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.
  • 18.
  • 19.
    Mendel’s Model • Mendeldeveloped a hypothesis to explain the 3:1 inheritance pattern he observed in F2 offspring • Four related concepts make up this model • These concepts can be related to what we now know about genes and chromosomes © 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.
  • 20.
    • First: alternativeversions of genes account for variations in inherited characters • For example, the gene for flower color in pea plants exists in two versions, one for purple flowers and the other for white flowers • These alternative versions of a gene are now called alleles • Each gene resides at a specific locus on a specific chromosome © 2011 Pearson Education, Inc.
  • 21.
    Figure 14.4 Allele forpurple flowers Locus for flower-color gene Allele for white flowers Pair of homologous chromosomes
  • 22.
    • Second: foreach character, an organism inherits two alleles, one from each parent • Mendel made this deduction without knowing about the role of chromosomes • The two alleles at a particular locus may be identical, as in the true-breeding plants of Mendel’s P generation • Alternatively, the two alleles at a locus may differ, as in the F1 hybrids © 2011 Pearson Education, Inc.
  • 23.
    • Third: ifthe two alleles at a locus differ, then one (the dominant allele) determines the organism’s appearance, and the other (the recessive allele) has no noticeable effect on appearance • In the flower-color example, the F1 plants had purple flowers because the allele for that trait is dominant © 2011 Pearson Education, Inc.
  • 24.
    • Fourth (nowknown as the law of segregation): the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes • Thus, an egg or a sperm gets only one of the two alleles that are present in the organism • This segregation of alleles corresponds to the distribution of homologous chromosomes to different gametes in meiosis © 2011 Pearson Education, Inc.
  • 25.
    • Mendel’s segregationmodel accounts for the 3:1 ratio he observed in the F2 generation of his numerous crosses • The possible combinations of sperm and egg can be shown using a Punnett square, a diagram for predicting the results of a genetic cross between individuals of known genetic makeup • A capital letter represents a dominant allele, and a lowercase letter represents a recessive allele © 2011 Pearson Education, Inc.
  • 26.
    Figure 14.5-1 P Generation Appearance: Geneticmakeup: Gametes: Purple flowers White flowers PP pp P p
  • 27.
    Figure 14.5-2 P Generation F1Generation Appearance: Genetic makeup: Gametes: Appearance: Genetic makeup: Gametes: Purple flowers White flowers Purple flowers Pp PP pp P P p p1 /2 1 /2
  • 28.
    Figure 14.5-3 P Generation F1Generation F2 Generation Appearance: Genetic makeup: Gametes: Appearance: Genetic makeup: Gametes: Purple flowers White flowers Purple flowers Sperm from F1 (Pp) plant Pp PP pp P P P P p p p p Eggs from F1 (Pp) plant PP ppPp Pp 1 /2 1 /2 3 : 1
  • 29.
    Useful Genetic Vocabulary •An organism with two identical alleles for a character is said to be homozygous for the gene controlling that character • An organism that has two different alleles for a gene is said to be heterozygous for the gene controlling that character • Unlike homozygotes, heterozygotes are not true-breeding © 2011 Pearson Education, Inc.
  • 30.
    • Because ofthe different effects of dominant and recessive alleles, an organism’s traits do not always reveal its genetic composition • Therefore, we distinguish between an organism’s phenotype, or physical appearance, and its genotype, or genetic makeup • In the example of flower color in pea plants, PP and Pp plants have the same phenotype (purple) but different genotypes © 2011 Pearson Education, Inc.
  • 31.
    Phenotype Purple Purple Purple White 3 1 1 1 2 Ratio 3:1 Ratio1:2:1 Genotype PP (homozygous) Pp (heterozygous) Pp (heterozygous) pp (homozygous) Figure 14.6
  • 32.
    The Testcross • Howcan we tell the genotype of an individual with the dominant phenotype? • Such an individual could be either homozygous dominant or heterozygous • The answer is to carry out a testcross: breeding the mystery individual with a homozygous recessive individual • If any offspring display the recessive phenotype, the mystery parent must be heterozygous © 2011 Pearson Education, Inc.
  • 33.
    Figure 14.7 Dominant phenotype, unknowngenotype: PP or Pp? Recessive phenotype, known genotype: pp Predictions If purple-flowered parent is PP If purple-flowered parent is Pp or Sperm Sperm Eggs Eggs or All offspring purple 1 /2 offspring purple and 1 /2 offspring white Pp Pp Pp Pp Pp Pp pp pp p p p p P P P p TECHNIQUE RESULTS
  • 34.
    The Law ofIndependent Assortment • Mendel derived the law of segregation by following a single character • The F1 offspring produced in this cross were monohybrids, individuals that are heterozygous for one character • A cross between such heterozygotes is called a monohybrid cross © 2011 Pearson Education, Inc.
  • 35.
    • Mendel identifiedhis second law of inheritance by following two characters at the same time • Crossing two true-breeding parents differing in two characters produces dihybrids in the F1 generation, heterozygous for both characters • A dihybrid cross, a cross between F1 dihybrids, can determine whether two characters are transmitted to offspring as a package or independently © 2011 Pearson Education, Inc.
  • 36.
    Figure 14.8 P Generation F1Generation Predictions Gametes EXPERIMENT RESULTS YYRR yyrr yrYR YyRr Hypothesis of dependent assortment Hypothesis of independent assortment Predicted offspring of F2 generation Sperm Sperm or Eggs Eggs Phenotypic ratio 3:1 Phenotypic ratio 9:3:3:1 Phenotypic ratio approximately 9:3:3:1315 108 101 32 1 /2 1 /2 1 /2 1 /2 1 /4 1 /4 1 /4 1 /4 1 /4 1 /4 1 /4 1 /4 9 /16 3 /16 3 /16 1 /16 YR YR YR YR yr yr yr yr 1 /4 3 /4 Yr Yr yR yR YYRR YyRr YyRr yyrr YYRR YYRr YyRR YyRr YYRr YYrr YyRr Yyrr YyRR YyRr yyRR yyRr YyRr Yyrr yyRr yyrr
  • 37.
    • Using adihybrid cross, Mendel developed the law of independent assortment • The law of independent assortment states that each pair of alleles segregates independently of each other pair of alleles during gamete formation • Strictly speaking, this law applies only to genes on different, nonhomologous chromosomes or those far apart on the same chromosome • Genes located near each other on the same chromosome tend to be inherited together © 2011 Pearson Education, Inc.
  • 38.
    Concept 14.2: Thelaws of probability govern Mendelian inheritance • Mendel’s laws of segregation and independent assortment reflect the rules of probability • When tossing a coin, the outcome of one toss has no impact on the outcome of the next toss • In the same way, the alleles of one gene segregate into gametes independently of another gene’s alleles © 2011 Pearson Education, Inc.
  • 39.
    • The multiplicationrule states that the probability that two or more independent events will occur together is the product of their individual probabilities • Probability in an F1 monohybrid cross can be determined using the multiplication rule • Segregation in a heterozygous plant is like flipping a coin: Each gamete has a chance of carrying the dominant allele and a chance of carrying the recessive allele The Multiplication and Addition Rules Applied to Monohybrid Crosses 1 2 1 2 © 2011 Pearson Education, Inc.
  • 40.
    Figure 14.9 Segregation of allelesinto eggs Segregation of alleles into sperm Sperm Eggs 1 /2 1 /2 1 /2 1 /2 1 /4 1 /4 1 /4 1 /4 Rr Rr R R R R R R r r r r r × r
  • 41.
    • The additionrule states that the probability that any one of two or more exclusive events will occur is calculated by adding together their individual probabilities • The rule of addition can be used to figure out the probability that an F2 plant from a monohybrid cross will be heterozygous rather than homozygous © 2011 Pearson Education, Inc.
  • 42.
    Solving Complex GeneticsProblems with the Rules of Probability • We can apply the multiplication and addition rules to predict the outcome of crosses involving multiple characters • A dihybrid or other multicharacter cross is equivalent to two or more independent monohybrid crosses occurring simultaneously • In calculating the chances for various genotypes, each character is considered separately, and then the individual probabilities are multiplied © 2011 Pearson Education, Inc.
  • 43.
    Figure 14.UN01 Probability ofYYRR Probability of YyRR 1 /4 (probability of YY) 1 /2 (Yy) 1 /4 (RR) 1 /4 (RR) 1 /16 1 /8 = × ×= = =
  • 44.
    Figure 14.UN02 Chance ofat least two recessive traits ppyyRr ppYyrr Ppyyrr PPyyrr ppyyrr 1 /4 (probability of pp) × 1 /2 (yy) × 1 /2 (Rr) 1 /4 × 1 /2 × 1 /2 1 /2 × 1 /2 × 1 /2 1 /4 × 1 /2 × 1 /2 1 /4 × 1 /2 × 1 /2 = 1 /16 = 1 /16 = 2 /16 = 1 /16 = 1 /16 = 6 /16 or 3 /8
  • 45.
    Concept 14.3: Inheritancepatterns are often more complex than predicted by simple Mendelian genetics • The relationship between genotype and phenotype is rarely as simple as in the pea plant characters Mendel studied • Many heritable characters are not determined by only one gene with two alleles • However, the basic principles of segregation and independent assortment apply even to more complex patterns of inheritance © 2011 Pearson Education, Inc.
  • 46.
    Extending Mendelian Geneticsfor a Single Gene • Inheritance of characters by a single gene may deviate from simple Mendelian patterns in the following situations: – When alleles are not completely dominant or recessive – When a gene has more than two alleles – When a gene produces multiple phenotypes © 2011 Pearson Education, Inc.
  • 47.
    Degrees of Dominance •Complete dominance occurs when phenotypes of the heterozygote and dominant homozygote are identical • In incomplete dominance, the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties • In codominance, two dominant alleles affect the phenotype in separate, distinguishable ways © 2011 Pearson Education, Inc.
  • 48.
    Figure 14.10-1 P Generation RedWhite Gametes CW CW CR CR CR CW
  • 49.
    Figure 14.10-2 P Generation F1Generation 1 /2 1 /2 Red White Gametes Pink Gametes CW CW CR CR CR CW CR CW CR CW
  • 50.
    Figure 14.10-3 P Generation F1Generation F2 Generation 1 /2 1 /2 1 /2 1 /2 1 /2 1 /2 Red White Gametes Pink Gametes Sperm Eggs CW CW CR CR CR CW CR CW CR CW CW CR CR CW CR CR CR CW CR CW CW CW
  • 51.
    • A dominantallele does not subdue a recessive allele; alleles don’t interact that way • Alleles are simply variations in a gene’s nucleotide sequence • For any character, dominance/recessiveness relationships of alleles depend on the level at which we examine the phenotype The Relation Between Dominance and Phenotype © 2011 Pearson Education, Inc.
  • 52.
    • Tay-Sachs diseaseis fatal; a dysfunctional enzyme causes an accumulation of lipids in the brain – At the organismal level, the allele is recessive – At the biochemical level, the phenotype (i.e., the enzyme activity level) is incompletely dominant – At the molecular level, the alleles are codominant © 2011 Pearson Education, Inc.
  • 53.
    Frequency of DominantAlleles • Dominant alleles are not necessarily more common in populations than recessive alleles • For example, one baby out of 400 in the United States is born with extra fingers or toes © 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.
  • 54.
    • The allelefor this unusual trait is dominant to the allele for the more common trait of five digits per appendage • In this example, the recessive allele is far more prevalent than the population’s dominant allele © 2011 Pearson Education, Inc.
  • 55.
    Multiple Alleles • Mostgenes exist in populations in more than two allelic forms • For example, the four phenotypes of the ABO blood group in humans are determined by three alleles for the enzyme (I) that attaches A or B carbohydrates to red blood cells: IA , IB , and i. • The enzyme encoded by the IA allele adds the A carbohydrate, whereas the enzyme encoded by the IB allele adds the B carbohydrate; the enzyme encoded by the i allele adds neither © 2011 Pearson Education, Inc.
  • 56.
    Figure 14.11 Carbohydrate Allele (a) Thethree alleles for the ABO blood groups and their carbohydrates (b) Blood group genotypes and phenotypes Genotype Red blood cell appearance Phenotype (blood group) A A B B AB none O IA IB i iiIA IBIA IA or IA i IB IB or IB i
  • 57.
    Pleiotropy • Most geneshave multiple phenotypic effects, a property called pleiotropy • For example, pleiotropic alleles are responsible for the multiple symptoms of certain hereditary diseases, such as cystic fibrosis and sickle-cell disease © 2011 Pearson Education, Inc.
  • 58.
    Extending Mendelian Geneticsfor Two or More Genes • Some traits may be determined by two or more genes © 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.
  • 59.
    Epistasis • In epistasis,a gene at one locus alters the phenotypic expression of a gene at a second locus • For example, in Labrador retrievers and many other mammals, coat color depends on two genes • One gene determines the pigment color (with alleles B for black and b for brown) • The other gene (with alleles C for color and c for no color) determines whether the pigment will be deposited in the hair © 2011 Pearson Education, Inc.
  • 60.
    Figure 14.12 Sperm Eggs 9 :3 : 4 1 /4 1 /4 1 /4 1 /4 1 /4 1 /4 1 /4 1 /4 BbEe BbEe BE BE bE bE Be Be be be BBEE BbEE BBEe BbEe BbEE bbEE BbEe bbEe BBEe BbEe BBee Bbee BbEe bbEe Bbee bbee
  • 61.
    Polygenic Inheritance • Quantitativecharacters are those that vary in the population along a continuum • Quantitative variation usually indicates polygenic inheritance, an additive effect of two or more genes on a single phenotype • Skin color in humans is an example of polygenic inheritance © 2011 Pearson Education, Inc.
  • 62.
    Figure 14.13 Eggs Sperm Phenotypes: Number of dark-skinalleles: 0 1 2 3 4 5 6 1 /8 1 /8 1 /8 1 /8 1 /8 1 /8 1 /8 1 /8 1 /8 1 /8 1 /8 1 /8 1 /8 1 /8 1 /8 1 /8 1 /64 6 /64 15 /64 20 /64 15 /64 6 /64 1 /64 AaBbCc AaBbCc
  • 63.
    Nature and Nurture:The Environmental Impact on Phenotype • Another departure from Mendelian genetics arises when the phenotype for a character depends on environment as well as genotype • The norm of reaction is the phenotypic range of a genotype influenced by the environment • For example, hydrangea flowers of the same genotype range from blue-violet to pink, depending on soil acidity © 2011 Pearson Education, Inc.
  • 64.
  • 65.
  • 66.
  • 67.
    • Norms ofreaction are generally broadest for polygenic characters • Such characters are called multifactorial because genetic and environmental factors collectively influence phenotype © 2011 Pearson Education, Inc.
  • 68.
    Integrating a MendelianView of Heredity and Variation • An organism’s phenotype includes its physical appearance, internal anatomy, physiology, and behavior • An organism’s phenotype reflects its overall genotype and unique environmental history © 2011 Pearson Education, Inc.
  • 69.
    Concept 14.4: Manyhuman traits follow Mendelian patterns of inheritance • Humans are not good subjects for genetic research – Generation time is too long – Parents produce relatively few offspring – Breeding experiments are unacceptable • However, basic Mendelian genetics endures as the foundation of human genetics © 2011 Pearson Education, Inc.
  • 70.
    Pedigree Analysis • Apedigree is a family tree that describes the interrelationships of parents and children across generations • Inheritance patterns of particular traits can be traced and described using pedigrees © 2011 Pearson Education, Inc.
  • 71.
    Figure 14.15 Key Male FemaleAffected male Affected female Mating Offspring 1st generation 2nd generation 3rd generation 1st generation 2nd generation 3rd generation Is a widow’s peak a dominant or recessive trait? (a) Is an attached earlobe a dominant or recessive trait? b) Widow’s peak No widow’s peak Attached earlobe Free earlobe FF or FfWW or Ww Ww ww ww Ww Ww Ww Wwww ww ww ww Ff Ff Ff Ff Ff ff ffffffFF or Ff ff
  • 72.
  • 73.
  • 74.
  • 75.
  • 76.
    • Pedigrees canalso be used to make predictions about future offspring • We can use the multiplication and addition rules to predict the probability of specific phenotypes © 2011 Pearson Education, Inc.
  • 77.
    Recessively Inherited Disorders •Many genetic disorders are inherited in a recessive manner • These range from relatively mild to life- threatening © 2011 Pearson Education, Inc.
  • 78.
    The Behavior ofRecessive Alleles • Recessively inherited disorders show up only in individuals homozygous for the allele • Carriers are heterozygous individuals who carry the recessive allele but are phenotypically normal; most individuals with recessive disorders are born to carrier parents • Albinism is a recessive condition characterized by a lack of pigmentation in skin and hair © 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.
  • 79.
  • 80.
  • 81.
    • If arecessive allele that causes a disease is rare, then the chance of two carriers meeting and mating is low • Consanguineous matings (i.e., matings between close relatives) increase the chance of mating between two carriers of the same rare allele • Most societies and cultures have laws or taboos against marriages between close relatives © 2011 Pearson Education, Inc.
  • 82.
    Cystic Fibrosis • Cysticfibrosis is the most common lethal genetic disease in the United States,striking one out of every 2,500 people of European descent • The cystic fibrosis allele results in defective or absent chloride transport channels in plasma membranes leading to a buildup of chloride ions outside the cell • Symptoms include mucus buildup in some internal organs and abnormal absorption of nutrients in the small intestine © 2011 Pearson Education, Inc.
  • 83.
    Sickle-Cell Disease: AGenetic Disorder with Evolutionary Implications • Sickle-cell disease affects one out of 400 African-Americans • The disease is caused by the substitution of a single amino acid in the hemoglobin protein in red blood cells • In homozygous individuals, all hemoglobin is abnormal (sickle-cell) • Symptoms include physical weakness, pain, organ damage, and even paralysis © 2011 Pearson Education, Inc.
  • 84.
    Fig. 14-UN1 © 2011Pearson Education, Inc. • Heterozygotes (said to have sickle-cell trait) are usually healthy but may suffer some symptoms • About one out of ten African Americans has sickle cell trait, an unusually high frequency of an allele with detrimental effects in homozygotes • Heterozygotes are less susceptible to the malaria parasite, so there is an advantage to being heterozygous
  • 85.
    Dominantly Inherited Disorders •Some human disorders are caused by dominant alleles • Dominant alleles that cause a lethal disease are rare and arise by mutation • Achondroplasia is a form of dwarfism caused by a rare dominant allele © 2011 Pearson Education, Inc.
  • 86.
  • 87.
  • 88.
    • The timingof onset of a disease significantly affects its inheritance • Huntington’s disease is a degenerative disease of the nervous system • The disease has no obvious phenotypic effects until the individual is about 35 to 40 years of age • Once the deterioration of the nervous system begins the condition is irreversible and fatal Huntington’s Disease: A Late-Onset Lethal Disease © 2011 Pearson Education, Inc.
  • 89.
    Multifactorial Disorders • Manydiseases, such as heart disease, diabetes, alcoholism, mental illnesses, and cancer have both genetic and environmental components • Little is understood about the genetic contribution to most multifactorial diseases © 2011 Pearson Education, Inc.
  • 90.
    Genetic Testing andCounseling • Genetic counselors can provide information to prospective parents concerned about a family history for a specific disease © 2011 Pearson Education, Inc.
  • 91.
    Counseling Based onMendelian Genetics and Probability Rules • Using family histories, genetic counselors help couples determine the odds that their children will have genetic disorders • Probabilities are predicted on the most accurate information at the time; predicted probabilities may change as new information is available © 2011 Pearson Education, Inc.
  • 92.
    Tests for IdentifyingCarriers • For a growing number of diseases, tests are available that identify carriers and help define the odds more accurately © 2011 Pearson Education, Inc.
  • 93.
  • 94.
    Fetal Testing • Inamniocentesis, the liquid that bathes the fetus is removed and tested • In chorionic villus sampling (CVS), a sample of the placenta is removed and tested • Other techniques, such as ultrasound and fetoscopy, allow fetal health to be assessed visually in utero © 2011 Pearson Education, Inc. Video: Ultrasound of Human Fetus I
  • 95.
    Figure 14.19 (a) Amniocentesis(b) Chorionic villus sampling (CVS) Ultrasound monitor Amniotic fluid withdrawn Fetus Placenta Uterus Cervix Centrifugation Fluid Fetal cells Several hours Several weeks Several weeks Biochemical and genetic tests Karyotyping Ultrasound monitor Fetus Placenta Chorionic villi Uterus Cervix Suction tube inserted through cervix Several hours Fetal cells Several hours 1 1 2 2 3
  • 96.
    Newborn Screening • Somegenetic disorders can be detected at birth by simple tests that are now routinely performed in most hospitals in the United States © 2011 Pearson Education, Inc.
  • 97.
    Figure 14.UN03 Complete dominance ofone allele Relationship among alleles of a single gene Description Example Incomplete dominance of either allele Codominance Multiple alleles Pleiotropy Heterozygous phenotype same as that of homo- zygous dominant Heterozygous phenotype intermediate between the two homozygous phenotypes Both phenotypes expressed in heterozygotes In the whole population, some genes have more than two alleles One gene is able to affect multiple phenotypic characters ABO blood group alleles Sickle-cell disease PP Pp CR CR CR CW CW CW IA IB IA , IB , i
  • 98.
    Figure 14.UN04 Epistasis Polygenic inheritance Relationshipamong two or more genes Description Example The phenotypic expression of one gene affects that of another A single phenotypic character is affected by two or more genes 9 : 3 : 4 BbEe BbEe BE BE bE bE Be Be be be AaBbCc AaBbCc
  • 99.
    Figure 14.UN05 Flower position Stemlength Seed shape Character Dominant Recessive Axial (A) Tall (T) Round (R) Terminal (a) Dwarf (t) Wrinkled (r)
  • 100.
  • 101.
    Figure 14.UN07 George Arlene SandraTom Sam Wilma Ann Michael Carla Daniel Alan Tina Christopher
  • 102.
  • 103.
  • 104.
  • 105.
  • 106.
  • 107.
  • 108.

Editor's Notes

  • #5 Figure 14.1 What principles of inheritance did Gregor Mendel discover by breeding garden pea plants?
  • #8 Figure 14.2 Research Method: Crossing Pea Plants
  • #9 Figure 14.2 Research Method: Crossing Pea Plants
  • #10 Figure 14.2 Research Method: Crossing Pea Plants
  • #14 Figure 14.3 Inquiry: When F1 hybrid pea plants self- or cross-pollinate, which traits appear in the F2 generation?
  • #15 Figure 14.3 Inquiry: When F1 hybrid pea plants self- or cross-pollinate, which traits appear in the F2 generation?
  • #16 Figure 14.3 Inquiry: When F1 hybrid pea plants self- or cross-pollinate, which traits appear in the F2 generation?
  • #19 Table 14.1 The Results of Mendel’s F1 Crosses for Seven Characters in Pea Plants
  • #22 Figure 14.4 Alleles, alternative versions of a gene.
  • #27 Figure 14.5 Mendel’s law of segregation.
  • #28 Figure 14.5 Mendel’s law of segregation.
  • #29 Figure 14.5 Mendel’s law of segregation.
  • #32 Figure 14.6 Phenotype versus genotype.
  • #34 Figure 14.7 Research Method: The Testcross
  • #37 Figure 14.8 Inquiry: Do the alleles for one character assort into gametes dependently or independently of the alleles for a different character?
  • #41 Figure 14.9 Segregation of alleles and fertilization as chance events.
  • #44 Figure 14.UN01 In-text figure, p. 270
  • #45 Figure 14.UN02 In-text figure, p. 270
  • #49 Figure 14.10 Incomplete dominance in snapdragon color.
  • #50 Figure 14.10 Incomplete dominance in snapdragon color.
  • #51 Figure 14.10 Incomplete dominance in snapdragon color.
  • #57 Figure 14.11 Multiple alleles for the ABO blood groups.
  • #61 Figure 14.12 An example of epistasis.
  • #63 Figure 14.13 A simplified model for polygenic inheritance of skin color.
  • #65 Figure 14.14 The effect of environment on phenotype.
  • #66 Figure 14.14 The effect of environment on phenotype.
  • #67 Figure 14.14 The effect of environment on phenotype.
  • #72 Figure 14.15 Pedigree analysis.
  • #73 Figure 14.15 Pedigree analysis.
  • #74 Figure 14.15 Pedigree analysis.
  • #75 Figure 14.15 Pedigree analysis.
  • #76 Figure 14.15 Pedigree analysis.
  • #80 Figure 14.16 Albinism: a recessive trait.
  • #81 Figure 14.16 Albinism: a recessive trait.
  • #87 Figure 14.17 Achondroplasia: a dominant trait.
  • #88 Figure 14.17 Achondroplasia: a dominant trait.
  • #94 Figure 14.18 Impact: Genetic Testing
  • #96 Figure 14.19 Testing a fetus for genetic disorders.
  • #98 Figure 14.UN03 Summary figure, Concept 14.3
  • #99 Figure 14.UN04 Summary figure, Concept 14.3
  • #100 Figure 14.UN05 Test Your Understanding, question 7
  • #101 Figure 14.UN06 Test Your Understanding, question 14
  • #102 Figure 14.UN07 Test Your Understanding, question 18
  • #103 Figure 14.UN08 Appendix A: answer to Figure 14.8 legend question
  • #104 Figure 14.UN09 Appendix A: answer to Figure 14.13 legend question
  • #105 Figure 14.UN10 Appendix A: answer to Concept Check 14.1, question 1
  • #106 Figure 14.UN11 Appendix A: answer to Concept Check 14.2, question 3
  • #107 Figure 14.UN12 Appendix A: answer to Summary of Concept 14.2 Draw It question
  • #108 Figure 14.UN13 Appendix A: answer to Test Your Understanding, question 2
  • #109 Figure 14.UN14 Appendix A: answer to Test Your Understanding, question 6