Notes: Sex-Linked Traits

1. Notes: Sex-Linked Traits

2. Sex-Linked Trait = Traits controlled by genes located on sex chromosomes

3. Females = XX, Males = XY

4. Sperm has 50%* of delivering X or Y chromosome to progeny

5. The X chromosome is large and contains about 2,000 genes. The Y chromosome is very small and has only86genes.

6. Mutations: • XXY - Klinefelter • XYY - “Super male” • XX male - during crossing over the gene that codes for testes moves to X chromosome

7. Small Y chromosome has 58 million base pairs • Evolving quickly, already 30% different than chimpanzee (high mutation rate due to storage in testes) • Contains no “vital” genes since Y is missing from female • Can contain diseases, most relating to testicular development

8. Genotypes written as XAXA (females) and XAY (males) • A = allele • Notice how some alleles only on X chromosome (sex linked)

9. Thomas Hunt Morgan studied fruit flies.

10. He crossed a white-eyed female (XrXr) with a red eyed male (XRY) XrXr XR Y

11. He crossed a white-eyed female (XrXr) with a red eyed male (XRY) XrXr XR Y

12. He crossed a white-eyed female (XrXr) with a red eyed male (XRY) XrXr XR Y Females: 100% Red eyed Males: 100% White eyed

13. Sex-Linked Disorders • Males are more likely to be affected, because females must inherit 2 bad copies of a gene to be affected, while males only need 1 bad copy

14. Sex-Linked Disorders • Males are more likely to be affected, because females must inherit 2 bad copies of a gene to be affected, while males only need 1 bad copy • Example: Color Blindness (b) is recessive to normal vision (B). Color blind female = XbXb Color blind male = XbY

15. Sex-Linked Disorders • Males are more likely to be affected, because females must inherit 2 bad copies of a gene to be affected, while males only need 1 bad copy • Example: Color Blindness (b) is recessive to normal vision (B). Color blind female = XbXb Color blind male = XbY • Other sex-linked disorders: Hemophilia, muscular dystrophy, baldness

16. You try: Breed a heterozygous female XBXb with a colorblind male XbY