1. CHAPTER 12 SEX-LINKED TRAITS
EQ: How can I determine the inheritance of a sex-linked trait?

2. Body Cells vs. Sex Cells
Autosomes: the first 22 homologous pairs of chromosomes.
Autosomes are the same for both males and females.
Sex cells: Determine sex of offspring

3. Is it Male or Female? Explain

4. Sex chromosomes: determines the sex of the individual.
The sex chromosomes are the 23rd pair of chromosomes. 
XX =female

5. XY=male

6. Which parent determines the sex of an offspring?
DAD
Why?
All moms have the genotype XX. When egg cells are made, they will all carry a single X chromosome.

7. All dads have the genotype XY
All dads have the genotype XY. When sperm cells are made, 50% will have an X chromosome and 50% will have a Y chromosome.
Therefore, males and females are born in roughly a 50:50 ratio.

8. SEX-LINKED TRAITS
Those traits that are controlled by genes on the X or Y chromosomes.
NOTE: The Y chromosome is much smaller than the X chromosome and only contains a few genes. Most sex-linked traits are on the X chromosome.

9. XH Xh XH XH XH Xh XH Y XH Y Xh Y male
In humans, hemophilia is a sex-linked trait.  Having hemophilia is recessive (Xh) to being normal (XH). The heterozygous female is called a carrier.  Cross a carrier female with a normal male. XH Xh
__ XHXh __  X  __ XHY ___
XH XH
XH Xh XH Y
male
XH Y
Xh Y

10. Results: Genotypic ratio: 1 XHXH :1 XHXh : 1 XHY :1 Xh Y
Phenotypic ratio: 2 normal females: 1normal male:
1 male with hemophilia XH Y
XH XH
Normal Female
XH Xh
Normal Female
Xh Y
Male w/ hemophilia
XH Y Normal Male

11. Now You Try Cross a carrier female with a male with hemophilia.
__ XHXh __  X  __ XhY ___

12. Results: Genotypic ratio: 1 XHXh :1 XhXh : 1 XHY :1 Xh Y
Phenotypic ratio: 1 normal female:
1 female w/ Hemopholia:
1normal male:
1 male with hemophilia
Xh Xh
Female w/ hemophilia XH Y
XH XH
Normal Female
Xh Y
Male w/ hemophilia
XH Y Normal Male

13. Genetic Sex-Linked Disorders Color Blindness
Cause: x-linked recessive
1/10 males have, 1/100 females have. Why the difference?
Individuals are unable to distinguish shades of red-green.

14. Genetic Sex-Linked Disorders
2- Hemophilia A and B
Recessive disorders that affect 1 of 5,000 males. These interfere with normal blood clotting and occur on the X chromosome.