Matters of Sex Genetic Disorders Related to the Sex Chromosomes

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

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

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

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

What is different?

Nondisjunction Disorders

Klinefelter’s Syndrome 47, XXY Due to Nondisjunction during meiosis 1: 500 - 1000 births Produce less testosterone Infertile or reduced fertility 48, XXXY 1:18000 - 50,000 births

Short, webbed neck, sterility, weak memory Turner’s Syndrome 45, X - Monosomy 1:2000 - 5000 births Short, webbed neck, sterility, weak memory Nondisjunction

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

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 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

Inheritance of Hemophilia

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