Red-green color blindness is X-linked recessive. A woman with normal color visio

Question

Red-green color blindness is X-linked recessive. A woman with normal color vision
has a father who is red-green color blind. The woman has four sons, none of whom are color blind. In this family there are no instances of chromosome loss or gain such as occurs due to non-disjunction in meiosis. Here are three explanations for why none of the sons are affected by color blindness. For each explanation, state if this explanation is valid or not and give the reason(s) for your choice.
a. Explanation 1: None of the sons are color blind because…the mother does not carry the color-blindness allele.

b. Explanation 2: None of the sons are color blind because…none of them inherited the color-blindness allele from the mother.

c. Explanation 3: None of the sons are color blind because…the mother inactivated the X chromosome with the recessive color-blindness

Explanation / Answer

a. not true because the grandfather has only one possible x chromosome to give to his daughter and that's the one with the gene for color blindness. The only way this can be true is if the mother is not his daughter biologically. b. is true. each son has a 50% chance of inheriting the x-chromosome with the gene for color blindness from his mother, as the mother is assumed to have one defective chrmosome and one good one. c. not true because x inactivation occurs only in somatic cells and does not affect the germline, which is where eggs come from.

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