Sexlinked Traits Sex determination Sex chromosomes determines the

Sex-linked Traits

Sex determination Ø Sex chromosomes – determines the sex of an individual ØY ØX Ø Males have X and Y ØTwo kinds of gametes Ø Female have two X’s ØOnly one type of gamete

Which parents determines the sex of the offspring? XY male X XX Y X Female X It is the male that determines the sex of the offspring.

Sex Linked Traits Ø Traits controlled by genes located on sex chromosomes (X or Y) Ø Most are X-linked ØThe X chromosome is larger and has more genes ØA Y has very few genes Ø Show inheritance pattern that differs for autosomal traits.

Ø Males only have one copy of the X chromosome (hemizygous), plus a Y Ø Female have two X chromosomes, and may be homozygous or heterozygous for a trait Ø X-linked genes are never passed from father to son. The Y chromosome is the only sex chromosome that passes from father to son.

ØFemales with one copy of the normal gene and one copy of the mutated gene are called carriers. They don’t show the trait. ØMales are never carriers – if they have a mutated gene on the X chromosome, it will be expressed

X-linked disorders Ø Recessive Ø Red-green color blindness Ø Hemophilia Ø Duchenne muscular dystrophy Ø Ichthyosis Ø Dominant Ø Hypertrichosis

Red-green color blindness ØCan not distinguish red from green. Normal red-green Red-green colorblind

What a red-green colorblind person would see Normal Red-green colorblind

Hemophilia

X Chromosome Inactivation Ø While females have two X chromosomes, only one is active. Ø The other is turned off. ØThis is random, in some cells the maternal X is turned off and in others the paternal X is turned off. ØAll descents of that cell will have same X turned off ØIt is condensed and known as a Barr Body.

Genes on the Y Chromosome Ø Few genes are on the Y chromosome Ø Hairy pinna