Question

Red-green color blindness is due to an X-linked recessive allele in humans. A widow�s peak (a hairline that comes to a peak in the middle of the forehead) is due to an autosomal dominant allele.

Consider the following family history:

• A man with a widow�s peak and normal color vision marries a color-blind woman with a straight hairline.

• The man�s father had a straight hairline, as did both of the woman�s parents.

Use the family history to make predictions about the couple�s children.

Drag the correct label to the appropriate location in the table. Not all labels will be used.

What is the chance that any daughter the couple has will be color blind with a straight hairline?	Drag answer here
What is the chance that any son that the couple has will be color blind with a widow's peak?	Drag answer here
If the couple has a child, what is the chance that it will be a daughter with a widow's peak?	Drag answer here
Suppose the couple had a daughter with normal color vision and a widow's peak.   What is the chance that she is homozygous for both genes?	Drag answer here

• 0

• 1/2

• 3/4

• 1

• 1/4
  
  

Answer 1

1) Son with widow's peak: 1/2 (probability of having a son) x 1/2 (probability of having Widow's Peak) = 1/4

2) Son, colour blind, straight hairline = 1 (probability of colour blind son) x 1/2 (probability of straight hairline)

3) Daughter, colour blind, widow's peak = 0 (all daughters will NOT be colour blind)

4) Daughter, normal vision, widow's peak = definitely heterozygous for normal vision (since she is a carrier) and definitely heterozygous for widow's peak (Ww), so chance she is heterozygous for both genes is 1.