Question

Colorblindness is a recessive X-linked (sex-linked) trait. What is the phenotypic ratio of the offspring if a man is colorblind and the woman is a carrier?

A) 1:1 (50% colorblind : 50% carrier)

B) 1:2 (25% colorblind : 75% carrier)

C) 1:1 (50% colorblind : 50% not colorblind)

D) 1:1:1:1 (25% colorblind : 25% carrier : 25% not colorblind : 25% not carrier)

Answer 1

The phenotypic ratio for the offspring of a colorblind man and a carrier woman is 1:1:1:1, with 25% chance for each being a carrier daughter, colorblind daughter, normal vision son, and colorblind son.

Step-by-step explanation:

Colorblindness is a recessive X-linked trait, which has different inheritance patterns for males and females due to the presence of XX chromosomes in females and XY chromosomes in males. If a man is colorblind (XcY) and the woman is a carrier (XCXc), there are different outcomes for male and female offspring. Using a Punnett square, we see that daughters (XCXc or XcXc) will have a 50% chance to be carriers and a 50% chance to be colorblind, and sons (XCY or XcY) will have a 50% chance to be colorblind and a 50% chance not to be colorblind.

The phenotypic ratio of the offspring is then 1:1:1:1, which corresponds to 25% carrier daughter, 25% colorblind daughter, 25% normal vision son, and 25% colorblind son. The correct answer to the question is D) 1:1:1:1 (25% colorblind: 25% carrier: 25% not colorblind: 25% not carrier).