Sex Linked Traits

1. Sex Linked Traits • Sex linked “traits” are determined by the genes located on the X or Y chromosome. • Genes found on the Y are related to sex determination (these genes make an embryo develop into a male)

2. Sex Linked Traits • Several thousand genes are found on the X chromosome, and only a few are related to the sex of an individual • The other genes code for non-sexual traits.

3. Sex Linked Genes • The Y chromosome is NOT homologous to the X chromosome. • Therefore, each male inherits only one copy of the genes found on the X chromosome • Since women inherit two X chromosomes, each female has two copies of the genes found on it.

4. Symbols • Sex linked genes are noted by writing the sex chromosomes and adding the gene (dominant or recessive) as an exponent. • XH= X-chromosome with dominant gene. • Xh= X-chromosome with recessive gene • Y = Y-chromosome without a gene for the trait

5. Sex Linked Genes • A woman is considered a carrier if she has one recessive sex-linked trait: XHXh • In a woman, the recessive trait is “hidden” by the dominant gene. • BUT if a man inherits one recessive sex-linked trait he always shows that trait: XhY

6. Sex Linked Genes on X Chromosome • Examples are: • Red/Green Colorblindness • Hemophilia – the Bleeding Disease • Duchenne’s Muscular Dystrophy

7. Sex Linked Genes • Complete worksheet problems 1-13!

8. Worksheet - Figure 1 • Woman carrier crossed with Normal Male XN Xn XN Y XNXN XNXn XNY XnY

9. Probabilities • Color blind daughter_________________ • Carrier daughter____________________ • Normal vision daughter non-carrier_____ • Color blind son_____________________ • Normal vision son___________________ O% 5O% 5O% 5O% 5O%

10. Sex Linked Genes • Complete worksheet problems 14-22

11. Figure 2 • Normal woman crossed with color blind Male XN XN Xn Y XN Xn XNXn XNY XNY

12. Probabilities • Color blind daughter_________________ • Carrier daughter____________________ • Normal vision daughter non-carrier_____ • Color blind son_____________________ • Normal vision son___________________ 0% 100% 0% 0% 100%

13. Figure 3 • Woman carrier crossed with Color Blind Male XN Xn Xn Y XNXn XnXn XNY XnY

14. Probabilities • Normal vision daughter _____ • Normal vision son___________________ 5O% 5O%

15. Sex Linked Genes • Complete worksheet problems 23-28

16. John Taylor’s Family • Begin with the information you are given. • What is John’s genotype?____________ • What is his brother’s genotype?_______ • What is his father’s genotype?________ XNY XnY XnY

17. John Taylor’s Parents XN Xn Xn Y XNXn XnXn XNY XnY

18. John Taylor’s Family • From which parent(s) did John’s brother inherit a gene for color blindness? • __________________________________ • From which parent(s) did John’s sister inherit a gene for color blindness? • __________________________________ mother father

19. John and Susie Taylor • Is it likely that they their son is colorblind? • Why or why not? NO