Final answer:
The mother was likely heterozygous for colorblindness, as the couple has a color-blind son who inherited the gene from her, and an unaffected daughter, while the father had normal color vision.
Step-by-step explanation:
Colorblindness is an X-linked recessive trait, meaning it is carried on the X chromosome and a male only needs one copy of the mutant gene to be affected. Females need two copies of the mutant gene to express the trait because they have two X chromosomes.
A color-blind son must have received the X chromosome with the colorblindness gene from his mother, while the unaffected daughter must have received a normal X from her mother and a normal Y from her father. This means that the mother must be a carrier of the colorblindness gene (i.e., heterozygous for colorblindness), and the father must have normal color vision since he cannot pass an X chromosome to his son. Therefore, the likely explanation is that the mother was heterozygous for colorblindness.
The son received the X chromosome carrying the colorblind gene from his mother and a Y chromosome from his father, resulting in colorblindness. The daughter received a normal X chromosome from her mother and she must receive a normal X from her father, because he does not have a condition to pass on.
The last statement in the student's question, that males can be carriers of red-green color blindness as it is autosomal recessive, is incorrect. Color blindness is not autosomal, but X-linked recessive; therefore, males cannot be carriers—they are either affected or not, based on the X chromosome they inherit from their mother.