Normal female, whose father was color blind married a normal man. What are the chances of color blindness in son
First, I need to recall that color blindness is an X-linked recessive trait. That means the gene responsible is on the X chromosome, and since it's recessive, a female needs two copies (X^cX^c) to express the condition, while males only need one (X^cY) because they have only one X chromosome.
The woman in question is normal, but her father was color blind. Since her father is X^cY, he must have passed his X^c to his daughter. Therefore, the woman is a carrier (X^CX^c). Her husband is normal, so his genotype is X^CY.
When they have children, the sons receive their X chromosome from the mother and Y from the father. The carrier mother can pass either X^C or X^c. The father contributes Y to the sons. So, there's a 50% chance the son gets X^c (from the mother) and becomes color blind (X^cY), and 50% chance of getting X^C (normal). Daughters would get X from mother and X from father, so they would be carriers if they get X^c, but since the father is normal, they would be X^CX^c (carrier) or X^CX^C (normal).
Looking at the answer choices, the correct one is 50% chance for the sons. The other options would be incorrect if they suggest different probabilities. For example, if an option says 0% or 25%, that's wrong because the mother is a carrier. If an option says 100%, that's also wrong because the father isn't a carrier. So, the correct answer is 50% for the sons.
**Core Concept**
Color blindness is an X-linked recessive disorder. Females (XX) require two mutated alleles (X^cX^c) to express the trait, while males (XY) need only one (X^cY). Carrier females (X^CX^c) transmit the defective allele to 50% of their offspring.
**Why the Correct Answer is Right**
The woman is a carrier (X^CX^c) because her father was color blind (X^cY) and her mother must have been a carrier (X^CX^c) or affected (X^cX^c). Her husband is unaffected (X^CY). Sons inherit the mother’s X chromosome and the father’s Y chromosome. There is a 50% chance the son receives the X^c allele from the mother, resulting in color blindness (X^cY). Daughters would inherit the father’s X^C allele, making them carriers (X^CX^c) but not affected.
**Why Each Wrong Option is Incorrect**
**Option A:** Suggests 0% chance, which is incorrect because the mother is a carrier.
**Option B:** Suggests 25% chance, which applies if both parents were carriers, but the father is unaffected.
**Option C:** Suggests 100% chance, which applies only if the mother were affected (