Sex inheritance. In humans, fruit flies, XX = female; XY = male. Inheritance of sex is just like any other trait, except it involve inheritance of an entire chromosome. Because there are genes on sex chromosomes, inheritance of certain traits can be sex-linked. Sex Linkage and Determination.
Because there are genes on sex chromosomes, inheritance of certain traits can be sex-linked.
Reciprocal cross produced a different result:
Inheritance of eye color depended on sex of the fly.
When the all red eyed F1 heterozygotes were crossed, close to a 3:1 ratio was observed, but the traits were not evenly divided between the sexes.
R = red eye
R = white eye
XX = female
XY = male
Carrier mother passes allele to son who expresses it, passes allele to daughter who carries it, etc.
Hemophilia & color blindness: examples in humans.
Homologues fail to separate during Meiosis I.
Sister chromatids fail to separate during Meiosis II.
Human Genome project has revealed much about the Y chromosome.
Descent of cells:
How mosaics are made.
Events during development.
Two homologous chromosomes, blue & red.
Black indicates inactivation = Barr body
Classic example: the calico cat.
One X chromosome codes for orange fur, the other for black. Cat shows characteristic mosaic patterns caused by one or the other X chromosome being inactivated.
White fur results from the effect of another gene.
Red: active genes.
Xic is responsible for this process; if moved to an autosome, that chromosome will be inactivated.