One form of night blindness is inherited as a recessive trait linked to the X chromosome.

One form of night blindness is inherited as a recessive trait linked to the X chromosome. Albinism is caused by an autosomal recessive gene. the spousal paronormal had a son with both anomalies on these two grounds. what is the likelihood that the second son in this family will also manifest both anomalies at the same time?

Let’s designate the chromosome with the night blindness gene as X k, then the gene that causes the development of normal twilight vision will be X K.

Let’s designate the gene for albinism as l, then the gene for normal pigmentation will be L.

A son born with both anomalies under consideration will have the X k Yll genotype, because homozygosity for albinism is a prerequisite for the realization of this recessive trait in the phenotype, and the Y chromosome does not carry a gene that prevents the expression of the night blindness gene.

Since the boy inherits the Y chromosome from his father, he receives the chromosome with the pathological gene X k from the mother, which allows us to conclude that the healthy mother is latent carriage of the pathological gene.

From each of the parents, the child inherits the albinism genes l, therefore, both parents are heterozygous for this trait – ll.

Thus, the mother has the genotype X K X k Ll. It is capable of producing four types of oocytes – X K L, X k l, X K l, X k L.

A healthy father has the genotype X K Y Ll and produces four types of spermatozoa – X K L, X K l, Y L, Y l.

The offspring of this married couple will be represented by the following possible options:

healthy girls (X K X K LL, 2X K X k Ll, 2X K X K L l, X K X k LL);

girls with albinism (X K X k ll, X K X K ll);

healthy boys (X K Y LL, 2 X K Y Ll);

boys with night blindness (2X k Y Ll, X k Y LL);

boys with night blindness and albinism (X k Y ll);

boys with albinism (X K Y ll).

A boy with night blindness and albinism – 1 genotype out of 16, which corresponds to 6.25%.

Answer: The probability of having a son with both anomalies in this family is 6.25%.