Ans: She must have at least one allele for color blindness
Explanation: Color blindness is a sex-linked gene (it’s found on the X chromosome) so for the son to have it, the mother must have an allele.
She mustn’t have two alleles before she can have it so the second option is wrong. Just one allele is enough for her son to have it.
It’s possible she’s homozygous recessive for the gene so the third option is wrong. As long as she has one allele or more, her son can get the gene.
She must be an heterozygous carrier for the gene, if not, she can’t pass it to her son. She must have an allele of color-blindness.
