Question

Pedigrees help geneticists understand how traits are inherited between generations. Red-green color blindness is a sex-linked disorder that is determined by a recessive allele on the X chromosome.
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If Brian has a son who is color-blind, what is known about the genotype of the son's mother?
She must have at least one allele for color blindness.
She must have two alleles for color blindness.
She cannot be homozygous recessive for the gene for color blindness.
She cannot be a heterozygous carrier of the gene for color blindness.

Answer 1

The answer is actually A. She must have at least one allele for color blindness. Just took the test

Answer 2

Red/green color blindness is passed down from mother to son and so we can conclude that the last two statements are wrong. Which are that "She cannot be homozygous recessive for the gene for color blindness" and "she cannot be a heterozygous carrier of the gene for color blindness "From the information proved we know that the mother must have at least one allele for color blindness.