A color-blind man marries a woman with nor- mal vision. Her mother was color-blind. They have one child. What is the chance that this child will be color-blind? (1) 0% ( 2 ) 25 % (3) 50% (4) 100%

To determine the chance that the child of a color-blind man and a woman with normal vision will also be color-blind, we need to consider the inheritance patterns of color blindness.

Color blindness is a sex-linked trait, meaning it is carried on the X chromosome. In this case, the woman's mother was color-blind, indicating that she carries the color-blindness gene on one of her X chromosomes.

Since the man is color-blind, he must have inherited the color-blindness gene from his mother. Therefore, he carries the color-blindness gene on his X chromosome as well.

When the couple has a child, there are several possibilities for the child's genotype:

1. If the child is a girl, she will inherit one X chromosome from her mother and one X chromosome from her father. If the father's X chromosome carries the color-blindness gene, and the mother's X chromosome also carries the color-blindness gene, then the child will be color-blind. This would occur in 25% of cases.

2. If the child is a boy, he will inherit one X chromosome from his mother and one Y chromosome from his father. Since the Y chromosome does not carry the color-blindness gene, the child's color vision will be determined solely by the X chromosome inherited from the mother. If the mother's X chromosome carries the color-blindness gene, then the child will be color-blind. This would also occur in 25% of cases.

Therefore, the chance that this child will be color-blind is 25%, which corresponds to option (2) in the given choices.