Transcript Sex Linked PPT - Old Saybrook Public Schools

Matters of Sex
Genetic Disorders
Related to the
Sex Chromosomes
Chromosome Pair #23
Men XY
Women XX
46, XY
X chromosome has ~ 1500 genes
Y chromosome has ~ 80 genes
46, XX
Does the mom or the dad determine
the sex of a child?
DAD
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
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
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
Inheritance of an
X linked Disorder
X Linked Disorders
• Colorblindness
• Hemophilia
• Duchenne Muscular Dystrophy
Colorblindness
Colorblindness Inheritance
6 % of men
0.4 % of women
Hemophilia
Normal gene on X codes
for clotting factors
1 : 10,000 men
1 : 100 million women
Queen Victoria passed the
mutation to the royal
bloodlines of Europe
Inheritance of Hemophilia
Muscular Dystrophy
Gene for dystrophin (muscle protein)
is mutated
1 : 3000 males