Final answer:
A son has a 50% probability of being colorblind if his mother carries one colorblind allele and the father has normal vision, as colorblindness is an X-linked recessive trait. A female would need to inherit two colorblind alleles to be affected, making it far less common in women.
Step-by-step explanation:
The probability of a son being colorblind when the mother has one allele for color blindness and one allele for normal vision, and the father has normal vision, is 50%. Colorblindness is an X-linked recessive trait, meaning it is linked to the X chromosome. Women have two X chromosomes (XX) and men have one X and one Y chromosome (XY). If a son inherits the X chromosome with the colorblind allele from his mother, he will express the trait because he has only one X chromosome.
For a female to express colorblindness, she would need to inherit two copies of the colorblind allele since it is recessive. This is highly unlikely, as it would require both her mother to be a carrier or affected, and her father to be affected. Since the trait is recessive, a woman can be a carrier without showing any symptoms if she has only one affected X chromosome. Girls with one normal and one colorblind allele are referred to as carriers, as the normal allele is dominant and masks the recessive trait.