Question

In humans, red-green color -blindness is a recessive X-linked trait. A man with red-green colorblindnes marries a normal-vision women whose father was color-blind. As the genitic counselor, construct a Punnett square to determine the genotypic and phenotypic possibilities of their children.

Answer 1

Let us consider ther 'X' as normal allele and 'Xc' as colourblind allele.

Asthe women has normal vision but her father was colourblind ,so she is a carrier which means she has one allele with colourblind trait. So her genotype is XXc and gamates formed by her will be X and Xc.

As the husband is colourblind so his genotype will be XcY and gamates produced by him will be Xc and Y.

So on mating the offspring will be of following genotype and phenotype:-

1. XXc-carrier female

2. XY-normal male

3. XcXc-colourblind female

4. XcY-colourblind male.

So there is possibility of all these offspring as shown above.

I think that will help.