Question

A man with normal vision marries a color-blind woman. Red-green color blindness is an X- linked recessive disorder. They have a daughter who has normal color vision. What is the probability that she is heterozygo

Answer 1

Answer: The probability is 100%.

Explanation: The chromosome X is related to gender. A man carries two different chromosomes (XY) and a woman carries two similar chromosomes (XX). The offspring of a couple will inherited:

• If it is a boy, he inherites the chromosome Y from his father and X from his mother;
• If it a girl, she inherites X from her father and X from her mother;

In the question, the woman is color-blind, which means she carries the recessive alleles: $X^{d}X^{d}$

The man, on the other hand, is normal, so his X-linked genotype will be: $X^{D}Y$.

Now, since they have a daughter, she inherited her double X from each of her parents, which means she inherited one $X^{d}$ from her mother and one $X^{D}$ from her father.

So, the daughter's genotype can only be heterozygotic  $X^{D}$$X^{d}$ in other words, the probability is 100%.