1. Matters of Sex
Genetic Disorders
Related to the
Sex Chromosomes

2. Chromosome Pair #23 Men XY Women XX 46, XY 46, XX
X chromosome has ~ 1500 genes
Y chromosome has ~ 80 genes

3. Does the mom or the dad determine the sex of a child?

4. How is sex determined? SRY gene
All fetuses begin as one sex regardless of the
sex chromosomes they have
At 6 weeks of development the SRY gene is switched on
SRY produces Testes Determining Factor
No SRY gene = female
Defective SRY gene = female 46, XY
Rarely the SRY gene is translocated to an X chromosome 46, XX male

5. Hermaphroditism Greek God Hermes and Goddess Aphrodite
Both sex organs (ovotestes)
Female masculinity forms when mother has excess testosterone while pregnant (ovarian tumors)
Male feminine forms due to problems with testosterone production because of malfunctioning of the SRY gene

6. X-linked Disorders X chromosome genes important for normal functioning
Women have 2 X chromosomes
Men have 1 X chromosome
Mutation in a gene on the X then a woman has a back-up copy a man does not, disorders more common in men
Man inherits his X from his mother

7. Inheritance of an X linked Disorder

8. X Linked Disorders Colorblindness Hemophilia
Duchenne Muscular Dystrophy

9. Colorblindness

10. Colorblindness Inheritance
6 % of men
0.4 % of women

11. Hemophilia Blood clotting disorder inability for blood to clot
Normal gene on X codes
for clotting factors
Blood clotting disorder inability for blood to clot
1 : 10,000 men
1 : 100 million women
Queen Victoria passed the mutation to the royal
bloodlines of Europe

12. Inheritance of Hemophilia

13. Gene for dystrophin (muscle protein)
Muscular Dystrophy
Gene for dystrophin (muscle protein)
is mutated
1 : 3000 males