Sex-linked Genes & Genetic Disorders

1. Sex-linked Genes & Genetic Disorders Unit 5: Genetics Ch. 11-3 & Parts of Ch. 14

2. Learning Goals • 1. Describe where sex-linked traits are located and and why these traits generally affect men more than women. Give an example of a sex-linked trait. • 2. Describe dominant and recessive disorders and give an example of each. • 3. Explain nondisjunction and how it leads to trisomy and monosomy.

3. Sex-Linked Genes X Chromosome • Some genes are carried on the sex chromosomes (X & Y) • XX = female, XY = male • Several disorders are carried on the X chromosome Y Chromosome

4. Because men have only 1 X, they don’t have a “backup” X like women • If the X is bad, men have the disease • EX: Colorblindness, hemophilia, muscular dystrophy

5. Color-Blindness • Three genes for color vision are located on the X chromosome. • In males, a defective version of any one of these genes produces colorblindness.

7. Sex-linked Crosses • 1) Must show sex chromosomes for each parent & alleles for each X chromosome • 2) Answer must include male or female

8. Predict Gender & Phenotypes • Colorblindness is a recessive trait • Geno: Pheno: • XCXC • XcXc • XCXc • XCY • XcY Normal Female Colorblind Female Normal / Carrier Female Normal Male Colorblind Male

10. Pedigree Charts • A chart used to examine the appearance of traits, especially diseases, over several generations.

11. Genetic Disorders • Some genes code for nonfunctional proteins. • These cause hereditary diseases.

12. Dominant Disorders • If you have the gene, you have the disease • May not show up until later in life, after you’ve had kids and passed it on • Huntington disease, Dwarfism

13. Huntington’s Disease • Results in the early death of some neurons in the brain. People loose the ability to control their movements. • Symptoms usually don’t start until the 20s to early 30s. • The disease is fatal, usually by the late 30s or early 40s.

15. Recessive Disorders • Can remain hidden and skip generations • Heterozygous individuals (Rr) are called “carriers” • Albinism, cystic fibrosis, Tay-Sachs, phenylketonuria

17. Cystic Fibrosis- Protein does not fold properly. Causes a build up of mucus in the lungs

18. Chromosomal Disorders • 1) Nondisjunction: chromosomes do not separate properly during meiosis • The results are cells with abnormal numbers of chromosomes. • Cells end up with extra chromosomes (47) or fewer chromosomes (45).

19. During Meiosis

20. Trisomy: If there are three homologous chromosomes instead of two • Down syndrome is caused by trisomy of chromosome 21

22. Where is the mutation?

23. Where is the mutation?

24. Monosomy: the cell is missing one chromosome • Turner’s syndrome is a female with one “X” chromosome not 2 “X” chromosomes.

26. 2) Alterations in Chromosome Structure • Deletion: portion of chromosome is deleted • EX: Cri du chat (Cry of the cat) • Duplication: piece of chromosome is repeated • Ex: Fragile X Syndrome • Translocation: piece of chromosome is deleted from one homologous pair and reattached to another homologous pair

27. Deletion: Cri du chat

28. Duplication: Fragile X

29. Translocation

30. Learning Goals • 1. Describe where sex-linked traits are located and why these traits generally affect men more than women. Give an example of a sex-linked trait. • 2. Describe dominant and recessive disorders and give an example of each. • 3. Explain nondisjunction and how it leads to trisomy and monosomy.

31. Whiteboard Practice • Legend & Parents • Punnett Square & Answers

32. Queen Victoria was a carrier of hemophilia (h), a recessive, sex-linked disease. King Edward was normal (H). • 1. Make a legend • 2. Genotypes of parents? • 3 & 4. Show the cross. • 5. Give probabilities for both sons and daughters

33. Muscular Dystrophy (d), is a recessive, sex-linked disease. A man who has muscular dystrophy marries a woman who is homozygous normal • 1. Make a legend • 2. Genotypes of parents? • 3 & 4. Show the cross. • 5. Give probabilities for both sons and daughters