Answer:
The correct answer is B. 25%.
Step-by-step explanation:
Color blindness is an inherited trait that is determined by genes on the X chromosome. Women have two X chromosomes, while men have one X and one Y chromosome. If a woman carries a gene for color blindness on one of her X chromosomes and a man with normal color vision marries her, their daughter has a 50% chance of inheriting the X chromosome with the color blindness gene from her mother. If the daughter inherits this X chromosome, she will be a carrier of the color blindness gene, but will not have color blindness herself because she also has a normal X chromosome from her father that will compensate for the effects of the color blindness gene. However, if the daughter later has a son, that son has a 50% chance of inheriting the color blindness gene from his mother and will be color-blind if he inherits it.
So in this scenario, the couple's daughter has a 50% chance of being a carrier of the color blindness gene, and their son has a 50% chance of being color-blind if they have one. Therefore, the overall probability of the couple having a color-blind daughter is 25%.
Here is a Punnett square illustrating the inheritance of the color blindness gene in this scenario:
| Normal color vision gene | Color blindness gene
-------|--------------------------|----------------------
Father | X |
Mother | X | X
-------|--------------------------|----------------------
Daughter| X | X
In this Punnett square, the capital letter X represents the X chromosome, and the small letters below it represent the genes that are carried on that chromosome. The father has one normal color vision gene (represented by the lowercase "x") on his X chromosome, and the mother has one normal color vision gene and one color blindness gene (represented by the lowercase "x" and "y", respectively) on her X chromosomes. The father's X chromosome is represented on the left side of the Punnett square, and the mother's X chromosomes are represented on the top.
Each of the boxes in the Punnett square represents a possible combination of X chromosomes that the couple's child could inherit. The child has a 50% chance of inheriting the father's X chromosome with the normal color vision gene and the mother's X chromosome with the normal color vision gene, a 50% chance of inheriting the father's X chromosome with the normal color vision gene and the mother's X chromosome with the color blindness gene, and a 0% chance of inheriting the mother's X chromosome with the color blindness gene and the father's X chromosome with the normal color vision gene (since the father does not carry the color blindness gene). If the child inherits the mother's X chromosome with the color blindness gene, she will be a carrier of the color blindness gene but will not have color blindness herself because she also has a normal X chromosome from her father that will compensate for the effects of the color blindness gene. If the child has a son, that son will have a 50% chance of inheriting the color blindness gene from his mother if she is a carrier.