Red-green color blindness is caused by an X-linked recessive gene. In a family, the mother is a carrier of this gene while the father does not have the gene. What are the possible effects on their children?
A. Half of the daughters are normal and half of the daughters are color-blind.
B. Half of the boys are normal and half of the boys are color-blind.
C. Half of the boys are color-blind and half of the girls are color-blind.

Question

Red-green color blindness is caused by an X-linked recessive gene. In a family, the mother is a carrier of this gene while the father does not have the gene. What are the possible effects on their children?
A. Half of the daughters are normal and half of the daughters are color-blind.
B. Half of the boys are normal and half of the boys are color-blind.
C. Half of the boys are color-blind and half of the girls are color-blind.

blues · Answer

You are told that the mother is a carrier but not color blind herself. If she had a color blind allele on both her X chromosomes, she would be color blind. That tells you that she is heterozygous: one of her chromosomes had the normal wild type allele and the other chromosome has the allele for color blindness.

The man is normal. That means he has an X with the normal wild type allele and a Y.

Using the parent's genotypes, you can do a Punnet Square to see what the offspring will be like.