Answer to Question #151127 in Microbiology for mike

Question

If a man with red-green colour blindness has a child with a woman who has normal colour vision and is homozygous for that gene, what is the probability that they will have a child who is red-green colour blind?

Answer 1

Red-green color blindness is X-linked meaning it cannot be found on the Y chromosome and women, in this case, can exhibit the state of heterozygous or homozygous while men can only be hemizygous.

Let X^c refer to red-green colorblindness. Note, c is recessive.

Let X⁺ refer to "normal". Note, + is dominant.

The woman has normal vision meaning she is heterozygous  X⁺X^c

Her husband is colorblind. Since he is hemizygous, his genotype must be: X^cY

The children this couple can produce we cross or fertilize the genotypes of the  father and mother

X^cY x X⁺X^c

X^c

Y

X⁺

X⁺X^c

X⁺Y

X^c

X^cX^c

X^cY

The probability that the first child from this marriage is color-blind  is a quarter