sex-linked traits 6

sex-linked characteristic

thomas hunt morgan

worked with D. melanogaster → exhibits XX-XY sex determination

discovers a single white-eyed male fly → set up crosses with true breeding wild type females (red eyes). the unusual results revealed X linked inheritance

x-linked inheritance

genes on the X chromosome

give different results from reciprocal crosses → males always inherit their X from the maternal line

y-linked inheritance

genes one the Y chromosome

all male offspring express the genotype of their fathers → females infected

dosage compensation

equalization of the amount of X-linked genes in males and females

double X expression in males - drosophila
halve X in females - X inactivation

barr body

Xist RNA

hemizygous

turner syndrome

X0 females → females with only one X chromosome

1/3000 female births

characteristics:
-short stature
-low hairline
-broad chest
-folds of skin on the neck
-normal intelligence

klinefelter syndrome

males with extra X chromosome(s) → XXY, XXXY, XXYY, XXXXY

1/1000 male births

characteristics:
-small testes
-reduced facial and pubic hair
-taller than normal
-normal intelligence

poly-x syndrome

females with more than two X chromosomes

1/000 females

tall and thin

more X’s more likely to be intellectually disable with a number of physical problems