Question

A colour-blind woman marries a man who is not colour-blind. All of their sons, but none of their daughters, are colour-blind. Which of the following statements correctly explains these results?

A) The gene for colour vision is incompletely dominant to the gene for sex determination.
B) The gene for colour vision is completely dominant to the gene for sex determination.
C) The gene for colour vision is codominant with the gene for sex determination.
D) The gene for colour vision is linked to the X chromosome.
E) The gene for colour vision is linked to the Y chromosome.

Answer 1

The correct answer is D) The gene for colour vision is linked to the X chromosome.

Step-by-step explanation:

Answer 2

The gene for color vision is linked to the X chromosome, making colorblindness an X-linked recessive inherited trait. Males with a defective gene on their single X chromosome express colorblindness, while females with two X chromosomes may carry the gene without expressing the condition.

Step-by-step explanation:

D) The gene for colour vision is linked to the X chromosome.

Colorblindness is a sexual-linked trait associated mainly with the X chromosome. Since males (XY) only have one X chromosome, any genes associated with color vision defects present on their sole X chromosome will be expressed. In contrast, females (XX) have two X chromosomes, meaning they have a backup copy which can mask the effects of a defective gene, rendering them typically non-expressing carriers unless both X chromosomes carry the colorblind gene.

This is why all the sons of this color-blind woman are colorblind—they each received her defected X chromosome, while the daughters, who received one normal X chromosome from their father, are not affected.

This pattern of inheritance explains the occurrence of color vision problems in the couple's children and is known as X-linked recessive inheritance.