Sex-Linked Genes Continued

On the X or the Y chromosome.

-Both x chromosomes have the same genes in the same places but the alleles will be different because of your parents.

The white-eyed fruit fly gene is attached to the x chromosome. If it was on the y chromosome all the males would have white eyes, that's not the case.
X^A = red
X^a = white
Y = no gene

*more women born than men because if they have as lethal recessive allele on the X chromosome, they will probably have a normal dominant gene on the other X chromosome. Men aren't protected because they only have one X chromosome.This leads to many male miscarriages as compared to few female miscarriages.

white eyed male = X^aY
red eyed female =X^AX^A

X^a (x) X^AX^A

       X^a           Y
X    X^AX^a     X^AY

let X^AY interbreed

Leads to two red eyed females, one red eyed male and one white eyed male.
Crossing a hetero female and a white eyed male creates one red eyed female, one red eyed male, one white eyed female, and one white eyed male.

Let's talk about human sex linked traits.
- colorblindness

A girls mother and father are normal, but her grandfather is colorblind. The mother is heterozygous with the dominant allele and the colorblind recessive allele. What are the odds of her brother having colorblindness? 1/2. What are the odds that her first child is colorblind? 1/8. Odds of first son being colorblind - 1/4.