In a family where parents have normal vision, the son is color blind. The genes for normal color vision (D) and color blindness (d) are located on the X chromosome. Gender and the likelihood of having children – carriers of the gene for color blindness.
Let’s designate the chromosome with the color blindness gene as Xd. The chromosome, which determines the development of normal color discrimination in a person, will be XD.
The son, a boy with color blindness, will be written as Xd Y. Since he inherits the chromosome with the abnormal gene (Xd) from the mother, it should be concluded that the mother is heterozygous for this gene. Let’s write it as XDXd, the eggs it produces as XD and Xd.
The boy’s healthy father will be XDY, and the sperm he produces will be XD and Y.
All possible offspring of this married couple will be represented by the following options:
healthy girls who are carriers of a pathological gene (XDXd) – 25%;
healthy girls (XDXD) – 25%;
healthy boys (XDY) – 25%;
boys with color blindness (Xd Y) – 25%.
Answer: girls are carriers, the probability of occurrence is 25%.
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