To understand the genotypes of the parents and the daughter regarding red-green color blindness, we need to consider the inheritance pattern of this sex-linked trait.
- Red-green color blindness is a recessive trait linked to the X chromosome (denoted as Xb for colorblindness and XB for normal vision).
- Males have one X and one Y chromosome (XY), while females have two X chromosomes (XX).
In this scenario:
- The colorblind male (father) must have the genotype XbY, since he is colorblind and has only one X chromosome.
- The mother, who has normal color vision, can be either homozygous normal (XX) or heterozygous (XBXb).
Since their daughter is colorblind, she must have inherited one colorblind X chromosome from her father (XbY). For her to be colorblind, she must also inherit a recessive X chromosome from her mother. This means that the mother must be heterozygous (XBXb) to pass on the colorblind allele (Xb).
Now we can summarize the genotypes:
- Father: Colorblind male has the genotype XbY.
- Mother: Normal vision female is heterozygous, with the genotype XBXb.
- Daughter: She is colorblind, having the genotype XbXb (homozygous recessive).
Given the options: a. The mother is heterozygous, father is colorblind, daughter is homozygous. (This is correct.) b. The mother is homozygous, father is homozygous, daughter is heterozygous. (Incorrect.) c. Impossible to determine with the given information. (Incorrect.) d. The mother is heterozygous, father is colorblind, daughter is heterozygous. (Incorrect.)
The correct answer is:
a. The mother is heterozygous, father is colorblind, daughter is homozygous.