[tammywammy]

ok i'm in ap biology this year, and i dont get genetics unit !

is there any websites that will help me be better at punnett squares. I'm really confused!



THE QUESTION~
A man with hemophilia(recessive, sex linked condition) has a daughter of normal phenotype. She marries a man who is normal for the trait. What is the probability that a daughter of this mating will be a hemophiliac? That a son will be a hemophiliac? If the couple has four sons, what is the probability that all four will be born with hemophilia?

I need to include cross ____x_____
punnett sqaure
and the gene+pheno%

THAnKYoU!!

[joie.de.vivre]

The first hemophiliac man is X^xY [because the condition is sex-linked and recessive (that's why there's a lowercase x on the X chromosome)/ sexlinked conditions are carried on the X chromosome).
His daughter, who doesn't have hemophilia, is X^XX^x (she doesn't have the condition because she's heterozygous...hemophilia can only occur in girls if both Xs have the recessive gene).
This girl marries a X^XY man, who doesn't have hemophilia (so he doesn't have the recessive gene at all).
If you make a punnett square of the above mating, then you'll end up with X^XX^X and X^XX^x (for the girls)...making the probablity 0 for a daughter of this matingn being a hemophiliac. The sons of this mating would be X^XY and X^xY..making the probablity of a hemophiliac son 50%.
The probablity for all four sons having hemophilia should be (.5)^4.