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![What is HOMOZYGOUS?
• Both alleles [forms of the gene]
are the same
• When offspring inherit two
dominant genes, (one dominant gene
from each parent) they are said to
be homozygous dominant
• When offspring inherit two
recessive genes, (one recessive
gene from each parent) they are
said to be homozygous recessive](https://image.slidesharecdn.com/4-171015140359/75/Biology-All-about-Genetics-17-2048.jpg)
Uploaded byPadme Amidala
Biology: All about Genetics
The document provides an overview of genetics, focusing on inheritance and the foundational work of Gregor Mendel, who studied traits in pea plants. It explains concepts such as dominant and recessive traits, alleles, genotypes, and phenotypes, as well as Mendel's laws of segregation and independent assortment. Various genetic terms and methods, including Punnett squares, are discussed to illustrate inheritance patterns and probabilities.
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Biology: All about Genetics
- 1.
- 2. HistoryHistory • GeneticsGenetics isthe study of genes.is the study of genes. • InheritanceInheritance is how traits, or characteristics,is how traits, or characteristics, are passed on from generation toare passed on from generation to generation.generation. • Chromosomes are made up of genes, whichChromosomes are made up of genes, which are made up of DNA.are made up of DNA. • Genetic material (genes,chromosomes,Genetic material (genes,chromosomes, DNA) is found inside the nucleus of a cell.DNA) is found inside the nucleus of a cell. • Gregor MendelGregor Mendel is considered “The Father ofis considered “The Father of Genetics"Genetics"
- 3. Gregor MendelGregor Mendel •Austrian Monk.Austrian Monk. • Experimented with “pea plants”.Experimented with “pea plants”. • Used pea plants because:Used pea plants because: – They were availableThey were available – They reproduced quicklyThey reproduced quickly – They showed obvious differences in the traitsThey showed obvious differences in the traits Understood that there was something thatUnderstood that there was something that carried traits from one generation to thecarried traits from one generation to the next- “next- “FACTORFACTOR”.”.
- 4. Mendel cont…… In themid-1800s, the rules underlying patterns of inheritance were uncovered in a series of experiments performed by an Austrian monk named Gregor Mendel.
- 5. Mendel's Plant BreedingExperiments Gregor Mendel was one of the first to apply an experimental approach to the question of inheritance. For seven years, Mendel bred pea plants and recorded inheritance patterns in the offspring. Particulate Hypothesis of Inheritance Parents pass on to their offspring separate and distinct factors (today called genes) that are responsible for inherited traits.
- 6. Mendel was fortunatehe chose the Garden Pea •Mendel probably chose to work with peas because they are available in many varieties. •The use of peas also gave Mendel strict control over which plants mated. •Fortunately, the pea traits are distinct and were clearly contrasting.
- 7. Mendel studies sevencharacteristics in the garden pea
- 8. Mendelian GeneticsMendelian Genetics •DominantDominant traits-traits- traits that are expressed.traits that are expressed. • RecessiveRecessive traits-traits- traits that are covered up.traits that are covered up. • Alleles-Alleles- the different forms of a characteristic.the different forms of a characteristic. • Punnett Squares-Punnett Squares- show how crosses areshow how crosses are made.made. • Probability-Probability- the chances/ percentages thatthe chances/ percentages that something will occur.something will occur. • Genotype-Genotype- the types of genes (Alleles)the types of genes (Alleles) present.present. • Phenotype-Phenotype- what it looks like.what it looks like. • Homozygous-Homozygous- two of the same alleles.two of the same alleles. • Heterozygous-Heterozygous- two different alleles.two different alleles.
- 9. Characteristics • These arefeatures you exhibit physically ( your looks) Example: Eye color - green
- 10. Traits • The differentversions of a characteristic • Example: blue, green, and brown eyes
- 11. Inheritance • Occurs whentraits are passed down from parent to child.
- 12. Genes • Bits ofinformation passed down from parent to child. • Made of chemicals called DNA.
- 13. Reproduction • Sexual –Sperm fertilizes an egg to produce offspring • Asexual – occurs when one organism copies itself to produce offspring
- 14. Fertilization • Occurs whena sperm unites with an egg
- 15. Offspring • Another namefor the children of a male and female parent
- 16. Alleles • T –is considered a dominant allele • t – is considered a recessive allele TT – is dominant Tt or tT – is dominant tt - is recessive
- 17. What is HOMOZYGOUS? •Both alleles [forms of the gene] are the same • When offspring inherit two dominant genes, (one dominant gene from each parent) they are said to be homozygous dominant • When offspring inherit two recessive genes, (one recessive gene from each parent) they are said to be homozygous recessive
- 18. What is HETEROZYGOUS? •When alleles occur in different forms • When offspring inherit one dominant gene and one recessive gene, they are said to be heterozygous • Since the dominant gene will be expressed, they are said to be heterozygous dominant
- 19. Genotype • A combinationof alleles Example: TT, Tt, or tt *We flipped coins to determine the genotype of our critters and puppies.
- 20. Genotype or Gamete •Genotype contains two copies of the gene. – AaBB • Gamete (sex cells) contains only one copy of the gene. – AB • Determine the possible gametes of AaBB – AB aB
- 21. Gamete or Genotype •State if its a gamete or genotype. • Aa • D • DdEeFFgg • sRtxyq • AaBBeeFF • adgEFT
- 22. List all thepossible gametes. • From the genotype AaBb • AB • Ab • aB • ab
- 23. Question #1Question #1 •How many different kinds of gametesgametes could the following individuals produce? 1.1. aaBbaaBb 2.2. CCDdeeCCDdee 3.3. AABbCcDDAABbCcDD 4.4. MmNnOoPpQqMmNnOoPpQq 5.5. UUVVWWXXYYZzUUVVWWXXYYZz
- 24. Question #1Question #1 •Remember the formula 2Remember the formula 2nn • Where n = # of heterozygousWhere n = # of heterozygous 1.1. aaBbaaBb = 2= 2 2.2. CCDdeeCCDdee = 2= 2 3.3. AABbCcDDAABbCcDD = 4= 4 4.4. MmNnOoPpQqMmNnOoPpQq = 32= 32 5.5. UUVVWWXXYYZzUUVVWWXXYYZz = 2= 2
- 25. Phenotype • They arethe traits determined by reading the genotype. • Example : FF = black fur • Black fur is the phenotype or trait
- 27. Punnett Square • Usesmom and dad’s genotypes to determine the possible traits of their offspring. • 4 offspring
- 28. Forked-line Method • Thismethod takes advantage of the Product Law, and exploits the fact that a cross can be broken down into a set of monohybrid crosses. • The forked line method is especially useful when three or more characteristics are crossed simultaneously.
- 30. LAWS OF MENDEL 1.Law of Segregation • Two alleles for a heritable character segregate (separate) during gamete formation and end up in different gametes.
- 31. • Mendel derivedthe law of segregation – By following a single trait • The F1 offspring produced in this cross – Were monohybrids, heterozygous for one character
- 32. • Does Mendel’ssegregation model account for the 3:1 ratio he observed in the F2 generation of his numerous crosses? – We can answer this question using a Punnett square
- 33. • Mendel’s lawof segregation, probability and the Punnett square Figure 14.5 P Generation F1 Generation F2 Generation P p P p P p P p PpPP ppPp Appearance: Genetic makeup: Purple flowers PP White flowers pp Purple flowers Pp Appearance: Genetic makeup: Gametes: Gametes: F1 sperm F1 eggs 1 /2 1 /2 Each true-breeding plant of the parental generation has identical alleles, PP or pp. Gametes (circles) each contain only one allele for the flower-color gene. In this case, every gamete produced by one parent has the same allele. Union of the parental gametes produces F1 hybrids having a Pp combination. Because the purple- flower allele is dominant, all these hybrids have purple flowers. When the hybrid plants produce gametes, the two alleles segregate, half the gametes receiving the P allele and the other half the p allele. 3 : 1 Random combination of the gametes results in the 3:1 ratio that Mendel observed in the F2 generation. This box, a Punnett square, shows all possible combinations of alleles in offspring that result from an F1 F1 (Pp Pp) cross. Each square represents an equally probable product of fertilization. For example, the bottom left box shows the genetic combination resulting from a p egg fertilized by a P sperm.
- 34. 2. Law ofIndependent Assortment •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
- 35. YYRRP Generation Gametes YRyr yyrr YyRr Hypothesis of dependent assortment Hypothesis of independent assortment F2 Generation (predicted offspring) 1 ⁄2 YR YR yr 1 ⁄2 1 ⁄2 1 ⁄2 yr YYRR YyRr yyrrYyRr 3 ⁄4 1 ⁄4 Sperm Eggs Phenotypic ratio 3:1 YR1 ⁄4 Yr1 ⁄4 yR1 ⁄4 yr1 ⁄4 9 ⁄16 3 ⁄16 3 ⁄16 1 ⁄16 YYRR YYRr YyRR YyRr YyrrYyRrYYrrYYrr YyRR YyRr yyRR yyRr yyrryyRrYyrrYyRr Phenotypic ratio 9:3:3:1 315 108 101 32 Phenotypic ratio approximately 9:3:3:1 F1 Generation Eggs YR Yr yR yr1 ⁄4 1 ⁄4 1 ⁄4 1 ⁄4 Sperm RESULTS CONCLUSION The results support the hypothesis of independent assortment. The alleles for seed color and seed shape sort into gametes independently of each other. EXPERIMENT Two true-breeding pea plants— one with yellow-round seeds and the other with green-wrinkled seeds—were crossed, producing dihybrid F1 plants. Self-pollination of the F1 dihybrids, which are heterozygous for both characters, produced the F2 generation. The two hypotheses predict different phenotypic ratios. Note that yellow color (Y) and round shape (R) are dominant. • A dihybrid cross – Illustrates the inheritance of two characters • Produces four phenotypes in the F2 generation Figure 14.8
- 36. • Using theinformation from a dihybrid cross, Mendel developed the law of independent assortment – Each pair of alleles segregates independently during gamete formation
- 37. Monohybrid Crosses 1.If onefruit fly is heterozygous (red) and the other is homozygous recessive (white), what percent of the offspring would be expected to have white eyes?
- 38. Monohybrid Crosses 2. Shorthair is dominant over long hair in guinea pigs. A short- haired guinea pig, one of whose parents was long-haired, was mated with a long- haired animal. What types of offspring could be produced? In what ratio?
- 39. Dihybrid Crosses 1. Blackfur in mice (B) is dominant to brown fur (b). Short tails (T) are dominant to long tails (t). What fraction of the progeny of the cross BbTt x BBtt will have black fur and long tails?
- 40. Dihybrid Crosses 2. Twotrue- breeding stocks of pea plants are crossed. One parent has red, axial flowers and the other, has white, terminal flowers; all F1 individuals have red, axial flowers. If 1000 F2 offspring resulted from the cross, approxiately how many of them would you expect to have red, terminal flowers?