Mom and Dad have two sons and two daughters. One son is red-green color-blind. What does this tell us about Mom and Dad?
A)Dad must be color-blind, because a son gets that gene from his father.
B)Mom must be color-blind and passed two recessive genes to her son.
C)Dad must be a carrier and passed the gene to his son.
D)Mom must be a carrier and passed the gene to her son.

Question

Quizplus · Accepted Answer

Red-green color blindness is a sex-linked recessive trait that is carried on the X chromosome. Since men only inherit one X chromosome from their mother, if the son is color-blind, he must have inherited the recessive gene from his mother. This means that Mom must be a carrier and passed the gene to her son. The father could either be color-blind himself or not affected but carrying the recessive gene.

Mom and Dad Have Two Sons and Two Daughters