Question

Albinism is known to be due to an autosomal recessive mutation. The first child of a couple with normal skin pigmentation was an albino. What is the probability that their second child will also be an albino?

• A. 0.5
• B. 0.75
• C. 1
• D. 0.25

Answer 1

The Correct Option is D

 To solve this problem, we need to understand the genetics behind albinism. Albinism is a condition characterized by the absence of pigment in the skin, hair, and eyes. This trait is caused by an autosomal recessive mutation.

An autosomal recessive mutation means that an individual must inherit two copies of the mutant allele (one from each parent) to express the trait. Let's use the following notation for the alleles:

• \(A\) - Normal allele (dominant)
• \(a\) - Mutant allele (recessive, causing albinism)

Individuals with normal pigmentation can have the following genotypes: \(AA\) (homozygous dominant) or \(Aa\) (heterozygous). Individuals with albinism must have the genotype \(aa\) (homozygous recessive).

For a child to be an albino (\(aa\)), each parent must at least carry one \(a\) allele. Given that the parents have normal pigmentation but their child is an albino, their genotypes must be \(Aa\).

Let's calculate the probability of having an albino child if both parents are \(Aa\) :

Using the Punnett square method, we have:

		\(A\)	\(a\)
\(A\)	\(A\)	\(AA\)	\(Aa\)
	\(a\)	\(Aa\)	\(aa\)

From the above Punnett square, the possible genotypes of their children are:

• \(AA\) - 25% (Normal pigmentation)
• \(Aa\) - 50% (Normal pigmentation, carrier)
• \(aa\) - 25% (Albino)

Therefore, the probability that their second child will also be an albino is \(0.25\) or 25%. This matches the correct option:

0.25

.