Question

Color blindness is a defect in vision of colors, this defect is due to a localize-homologous segment of chromosome X.

In the document I have a pedigree which the parents and their children are normal; but then most of the children got married to a diseased one which 50% produced are diseased.

question: Is the allele responsible for color blindness dominant or recessive? Justify your answer.

The allele responsible for color blindness is recessive, but how do we justify?

Answer 1

Let N = normal allele and b = colorblind

Parents are XNY and XNXb

Only the girls in the first generation carried the b. If the boys had the b, they would be colorblind, because there would be no N on the Y chromosome.

To produce 50% colorblind, the males must have married colorblind females, so all of the male grandchildren would be colorblind and all of female grandchildren would be carriers.

Do a Punnett Square.

https://www.google.com/search?client=safari&rls=en&q=punnett+square&ie=UTF-8&oe=UTF-8&gws_rd=ssl