Chapter 12 human genetics

I. Human Heredity A. Human chromosomes 1. A picture of chromosomes arranged in a picture is called a karyotype.

2. A normal human has 46 chromosomes, 23 pairs. 3. The number of chromosomes helps identify what the organism is. 4. Egg and sperm are haploid, containing half the amount of chromosomes-23. These cells are called sex cells. A female chromosomes is XX, a male is XY.

5. All other cells have 46 chromosomes in them, they are diploid. These cells are called autosomes. 6. All human egg cells carry a single X chromosome.

7. Half of all sperm cells carry an X and half carry a Y chromosome. 8. This ensures that just about half of the zygotes will be 46XX and the other half will be 46XY.

B. Human Traits 1. Human genes are inherited according to the same principals that Mendel discovered. 2. A pedigree chart shows relationships within a family.

3. Genetic counselors analyze pedigree charts to infer the genotypes of family members. 4. Many traits are strongly influenced by environmental, or non-genetic factors, including nutrition and exercise.

C. Human Genes 1. The human genome- our complete set of genetic information includes tens of thousands of genes. 2. Some of the very first genes to be identified were those that control blood type.

D. Blood Group Genes 1. Human blood comes in a variety of genetically determined blood groups. 2. The different blood types are A, B, AB O plus there is a Rh+ or Rh- factor.

BLOOD GROUPS Phenotype Genotype Antigen Antibodies A I A I A or I A I o A B B I B I B or I B I o B A AB I A I B A and B ------- O I o I o -------- A and B

E. Recessive Alleles 1. Many human genes have become known through the study of genetic disorders. 2. In most cases genetic disorders are USUALLY recessive. 3. See page 345 to see some disorders

F. Dominant Alleles 1. Not all genetic disorders are caused by a recessive allele. 2. Two examples of a genetic disorder caused by autosomal dominant alleles are dwarfism and Huntington ’ s disease.

G. Codominant alleles 1. Sickle cell disease is caused by a codominant allele.

H. From Gene to molecule 1. In both cystic fibrosis and sickle cell disease, a small change in the DNA of a single gene affects the structure of a protein, causing a series genetic disorder. 2. CF is most common among people with Northern Europe ancestors.

3. People with CF have serious digestive problems in addition they produce thick, heavy mucus that clogs their lungs and breathing passageways. 4. Sickle cell is a disease found in African American ’ s.

3. It is a bent and twisted shape of the RBC ’ s. 4. As a result, blood stops moving through these vessels, damaging cells, tissues and organs. 5. Sickle cell disease produces physical weakness, and damage to the brain, heart, and spleen.

II. Human Chromosomes A. Human Genes and Chromosomes 1. Chromosomes 21 and 22 are the smallest human autosomes. Chromosome 22 contains 43 million DNA base pairs! Chromsomes 21 contains about 32 million! 2. MILLIONS of base pairs!

B. Sex Linked Genes 1. Many sex-linked genes are found on the X chromosomes. More than 100 sex-linked genetic disorders are found on the X. 2. Males have just one X chromosome, thus all X-linked alleles are expressed in males even if they are recessive.

3. Some sex-linked disorders are colorblindness, hemophilia, and Duchenne muscular dystrophy.

C. Color Blindness 1. The most common disorder is red-green colorblindness affecting 1 in 10 males in the US. 2. Among females colorblindness is only 1-100.

D. Hemophilia 1. Two important genes carried on the X chromosome help blood to clot. 2. In hemophilia, a protein necessary for normal blood clotting is missing. 3. About 1 in 10,000 males is born with hemophilia.

E. Duschenne Muscular dystrophy 1. This is a disorder that results in the progressive weakening and loss of skeletal muscles. 2. In the US 1 out of 3000 males are born with this.

F. X-Chromosome Inactivation 1. Females have 2 X chromosomes, but males have only 1. 2. In female cells, one X chromosome is randomly switched off.

G. Chromosomal disorders 1. The most common error in meiosis occurs when homologous chromosomes fail to separate. This is known as nondisjunction. 2. If nondisjunction occurs, abnormal numbers of chromosomes may find their way into gametes, and a disorder of chromosome numbers may result.

3. IF two copies of an autosomal chromosome fail to separate during meiosis, an individual may be born with three copies of a chromosome. 4. This is known as trisomy

5. The most common trisomy is down syndrome- having an extra chromosome on pair number 21. 6. 1-800 babies are born with Down syndrome.

7. Disorders also occur among the sex chromosomes. Two of these are Turner syndrome and Klienefelter ’ s. 8. In Turner syndrome there is only 1 X. The female is sterile and their sex organs do not develop at puberty.

9. In males, Klinefelter ’ s has an extra X, XXY, XXXY or even XXXXY.

10. There have been no reported cases of babies being born without the X chromosome, indicating that the X chromosome contains genets that are vital for the survival and development.

III. Human Molecular Genetics A. Human DNA analysis 1. DNA fingerprinting is used by molecular biology to identify individuals.

2. The human genome project is an ongoing effort to analyze the human DNA sequence. 3. In gene therapy, an absent or faulty gene is replaced by a normal, working gene.

4. It would be great to cure genetic disorders= BUT, if human cells can be manipulated to cure disease, should biologists try to engineer taller people or change their eye color, ect?

Chapter 12 human genetics

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Chapter 12 human genetics