Question

The first child of a normal pigmented couple is albino. The possibility of a second child being an albino is:

• A. 25%
• B. 50%
• C. 75%
• D. 100%

Answer 1

The correct option is A 25%

Albinism is an autosomal recessive disease. Suppose,

• A=allele of dominant normal pigment
• a=allele of recessive albino pigment

The first child being an albino (aa genotype) while the parents are normal, is only possible when both the parents are heterozygous (Aa).

So, the cross between parents is Aa X Aa, which in turn gives:

Gametes	A	a
A	AA (normal)	Aa (normal)
a	Aa (normal)	aa (albino)

There is a possibility of one child out of 4 to be an albino. Therefore, the possibility of a second child being an albino is $\frac{1}{4}\times 100\%$ = 25%.