Answer to Question #145481 in Genetics for Vaith

Question

The gene of daltonism is recessive X-linked. Woman with normal sight, whose father had daltonism, got married to sick man. Determine the phenotypes and genotypes of children in this family, and the probability of birth of healthy children.

Answer 1

Let the gene for Daltonism be d, therefore, that for normal sight is D

Since the gene is x-linked, then the father to the woman was X^dY, and since the woman inherited one X chromosome from the father, then the woman was a carrier (X^dX^D).

The husband to the woman was therefore X^dY

Genetic cross will look like this;

Parental genotypes: X^dX^D x X^dY

Gametes:

Punnet square;

Female

male X^d X^D

X^d X^d X^d X^DX^d

Y X^dY X^DY

Phenotypes of the children;

X^d X^d = Daltonism/sick girl

X^DX^d = Normal sight(Carrier) girl

X^dY = Daltonism/sick boy

X^DY = Normal sight boy

Probability of getting normal children;

P(normal) =$\dfrac{normal children}{total possible children}=\dfrac{2}{4}$ x 100 = 50%