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

2. Karyotypes Female 46, XX Male 46, XY
Photograph of homologous chromosomes, arranged by size (largest to smallest), shape, centromere location
Female 46, XX
Male 46, XY

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

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

5. 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

6. 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

7. What is different?

8. Nondisjunction Disorders

9. Klinefelter’s Syndrome
47, XXY
Due to Nondisjunction during meiosis
1: births
Produce less testosterone
Infertile or reduced fertility
48, XXXY 1: ,000 births

10. Short, webbed neck, sterility, weak memory
Turner’s Syndrome
45, X - Monosomy
1: births
Short, webbed neck, sterility, weak memory
Nondisjunction

11. 47, XYY / Super Male Slightly taller, normal fertility 1:1000 births
47, XXX / Triple X (Super Female)
No observable differences
1:1000 births
May be taller with mild learning difficulties

12. 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

13. Inheritance of an X linked Disorder

14. X Linked Disorders Colorblindness Hemophilia
Duchenne Muscular Dystrophy

15. Colorblindness

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

17. 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

18. Inheritance of Hemophilia

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