1. Sex-Linked
Inheritance

2. Sex Determination X X X Y X X X X X Y X Y
Sex determined by genes found on the X and Y chromosome
Females: egg produced with an X chromosome
Males: ½ sperm cells contain X; and the other ½ contain Y
There is a 50/50 chance of child being a boy/girl

3. Sex-Linked Disorders
Defined: Inherited conditions found on X chromosome
Usually recessive
Females: XX chromosomes
XH XH = healthy
XH Xh = healthy carrier
Xh Xh = disease
Males: XY chromosomes
XHY = healthy
XhY = disease
Rare in women (back-up X chromosome)
Ex: Colorblindness, Hemophilia, Muscular dystrophy

4. Sample Colorblind Tests

5. Sample Colorblind Tests
4 Sex-Linked Traits:   1. Normal Color Vision:  A: 29,  B: 45,  C: --,  D: 26   2. Red-Green Color-Blind:  A: 70,  B: --,  C: 5,  D: --   3. Red Color-blind:  A: 70,  B: --,  C: 5,  D: 6   4. Green Color-Blind:  A: 70,  B: --,  C: 5,  D: 2

6. 1 min: Discuss with your neighbor
1 min: Discuss with your neighbor. Jen is a healthy carrier (XH Xh) of hemophilia and Adam has no history in his family (XH Y).
What is the probability of:
a. Daughter with hemophilia? 0%
b. Carrier child?
25%
c. Child with hemophilia?
d. All healthy children?
75%
Healthy girl
Healthy boy
Healthy girl (carrier)
Hemophiliac boy

7. Kelly does not have hemophilia even though her mother did
Kelly does not have hemophilia even though her mother did. Jim (Kelly’s husband) is a hemophiliac. Their first child Barry is healthy but their other child Rachel is a hemophiliac. Draw a Pedigree for this family and a Punnett square for Jim and Kelly.
Kelly’s
mother
What is the probability of getting a:
a. Healthy son?
50%
b. Healthy daughter?
c. Child with hemophilia?
d. Carrier child?
25%
Kelly
Jim
Barry
Rachel
Healthy girl (carrier)
Healthy boy
Hemophiliac girl
Hemophiliac boy

8. Review How are sex-linked disorders different from autosome disorders?
Why are sex-linked disorders more common in males?
Write the genotype of a heterozygous dominant female.
Write the genotype of a carrier female.
Examine Kelly and Jim’s Punnett square. What are the chances they would have three children, all of whom are healthy?