Final answer:
The probability that a son of a couple, where the mother is a carrier for red-green color blindness and the father is affected, will be color-blind is 50% or 1 in 2 (answer e. 1/2). This is because the son has an equal chance of inheriting the mother's normal or color-blind X chromosome and will always inherit the father's Y chromosome.
Step-by-step explanation:
The subject of the question is Biology, specifically genetics and the inheritance of color blindness, which is an X-linked recessive trait. According to the information provided, we are asked to calculate the probability that a son of a couple, where the mother is a carrier for red-green color blindness and the father is affected by it, will also be color-blind. Since the mother has one normal allele and one allele for color blindness (her father was color-blind), she is a carrier. The father has only one X chromosome with the allele for color blindness.
When we construct a Punnett square for this cross, we get the following possibilities for a son:
- XCY (Normal vision) from the mother's normal X chromosome and the father's Y chromosome.
- XcY (Color blind) from the mother's colorblind X chromosome and the father's Y chromosome.
There is a 50% chance (1 in 2) that a son will be color-blind because he has a 50% chance of inheriting the X chromosome carrying the color-blind allele from his carrier mother and a 100% chance of inheriting a Y chromosome from his father, which does not carry an allele for color vision at all.
The correct answer to the question is e. 1/2.