Phoebe's mother is red-green colorblind and her father is not. what is the probability that phoebe's son is red-green colorblind?

The correct answer would be 50% .

Red-green colorblindness is an X-linked recessive disorder that is, the mutated gene responsible for this trait is present on the X chromosome.

Let the "R" and "r" be the alleles of the gene responsible for this trait.  

R is the dominant trait which leads to the normal vision in a person. Thus, heterozygotes will have a normal vision however, they will act as the carrier of the disease.

r is the recessive allele which causes red-green colorblindness in a person when present in homozygous condition.

Now, the genotype of the mother with red-green colorblindness would be and the genotype of unaffected father would be .

The cross will result in the production of two daughters each heterozygous and two sons each with the colorblindness.  

The probability of having a son = 1/2.

The probability of son being colorblind = 1

Thus, the probability of having a son with colorblindness = 1/2 x 1 = 1/2 or 50%

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