1. Sex-Linked
Inheritance

2. Sex Determination
Sex determined by genes found on the X and Y chromosome
Females: egg produced with an X chromosome

3. Sex Determination
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

4. 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
X X
50% Girl X Y X X X X
50% Boy X Y X Y

5. Sex-Linked Disorders XH XH XH Y XH Xh Xh Y Xh Xh
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)
XH XH
XH Y
XH Xh
Xh Y
Xh Xh
H = healthy h = disorder

6. Duchene Muscular Dystrophy
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)
Examples of disorders:
Duchene Muscular Dystrophy
Hemophilia
Colorblindness

7. Types of Colorblindness

8. Normal
Deuteranopia (2.7%)

9. Normal
Protanopia (0.59%)

10. Normal
Tritanopia (0.016%)

11. Colorblind Test: Do you see a number inside the picture?53

12. Colorblind Test: Do you see a number inside the picture?12

13. Colorblind Test: Do you see a number inside the picture?6

14. Colorblind Test: Do you see a number inside the picture?74

15. Colorblind Test: Do you see a number inside the picture?6

16. Hemophilia and the Royal Family

17. 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. Two healthy children?
9/16 (56%)
Healthy girl
Healthy boy
Healthy girl (carrier)
Hemophiliac boy
2010
2013 x

18. Hemophilia is a sex linked disorder
Hemophilia is a sex linked disorder. 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.
Xh Xh
What is the probability of getting a:
a. Healthy son?
25%
b. Healthy daughter?
c. Child with hemophilia?
50%
d. Carrier child?
Kelly’s
mother
Kelly
Jim XH Xh
Xh Y
Barry
Rachel
Healthy girl (carrier)
Healthy boy
XH Y
Xh Xh
Hemophiliac girl
Hemophiliac boy

19. Sex linked recessive: Hemophilia
Key
XH = healthy
Xh = hemophilia
Sex linked recessive: Hemophilia 1 7 2 3 4 6 5 8 14 10 11 12 9 13
XH Y
XH Y
Xh Y
XH Y
XH Y
XH Y
Males:
XH Y or
Xh Y
XH Y
Xh Y
Xh Y
Hint: Only 1 person is unknown.

20. Sex linked recessive: Hemophilia
Key
XH = healthy
Xh = hemophilia
Sex linked recessive: Hemophilia 1 7 2 3 4 6 5 8 14 10 11 12 9 13 Y Xh
XH Y XH Xh
XH Y
Xh Y
XH Y XH XH
from mother
from father
Females:
XHXH or
XHXh
XhXh
XH Y
XH Y
Xh Y XH
XH Y XH
Xh Y
Hint: Only 1 person is unknown.

21. Sex linked recessive: Hemophilia
Key
XH = healthy
Xh = hemophilia
Sex linked recessive: Hemophilia 1 7 2 3 4 6 5 8 14 10 11 12 9 13
XH Y XH Xh Xh Y
XH Y
Xh Y
XH Y XH XH Xh
Females:
XHXH or
XHXh
XhXh
XH Y
XH Y XH
XH Y
Xh Y XH
from mother
from father
Xh Y
Hint: Only 1 person is unknown.

22. Sex linked recessive: Hemophilia
Key
XH = healthy
Xh = hemophilia
Sex linked recessive: Hemophilia 1 7 2 3 4 6 5 8 14 10 11 12 9 13
XH Y XH Xh
XH Y
Xh Y
XH Y XH XH Xh Y Xh
Females:
XHXH or
XHXh
XhXh
XH Y
XH Y XH
XH Y
Xh Y Xh XH
Xh Y
from mother
from father

23. Sex linked recessive: Hemophilia
Key
XH = healthy
Xh = hemophilia
Sex linked recessive: Hemophilia 1 7 2 3 4 6 5 8 14 10 11 12 9 13
XH Y XH Xh Xh XH
XH Y
Xh Y
XH Y XH Xh XH Xh
Females:
XHXH or
XHXh
XhXh
XH Y
XH Y XH
XH Y
Xh Y Xh XH
from father
from mother
Xh Y
Hint: Only 1 person is unknown.

24. Sex linked recessive: Hemophilia
Key
XH = healthy
Xh = hemophilia
Sex linked recessive: Hemophilia 1 7 2 3 4 6 5 8 14 10 11 12 9 13
XH Y XH Xh XH
XH Y
Xh Y
XH Y XH Xh XH Xh
Females:
XHXH or
XHXh
XhXh
XH Y
XH Y XH
XH Y
Xh Y Xh XH X?
from father
from mother
Xh Y
Hint: Only 1 person is unknown.

25. Quiz How are sex-linked disorders different from autosome disorders?
Why are sex-linked disorders more common in males?
Write the genotype of a heterozygous 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?