A man who has pattern baldness married a woman who is a carrier for the trait. What percent of their male children would be expected to develop male pattern baldness as adults?

A 25%

B 0%

C 50%

D 100%

C. 50%

Explanation:

Baldness is sex-linked, so we need to use the X and Y chromosome notation. Let's represent baldness with B, and no baldness as b.

Man: XB Y

Woman: XB Xb

(Remember, she's a carrier: so she has one B allele, but not both, otherwise she would express the trait.)

What's next - Punnett square, our old buddy:

XB Y

XB XB XB XB Y

Xb XB Xb Xb Y

So out of that square, they've got two males. That's our denominator. And it wants to know how many male progeny will be bald: that's only one, the one with XB Y. He will express the B allele because the Y's kinda just like a placeholder. So the probability is 50%.