Question

Albinism is known to occur 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. 100%
B. 25%
C. 50%
D. 75%

Answer 1

Albinism is a rare genetic disorder characterized by no color or very little color in skin, hair or eyes of the person. The person having this disorder may suffer from vision problems. The lack of skin pigments also makes the person more susceptible to skin burn and cancers.

Complete answer: Genetic mutations are the changes in the gene and its expressions while chromosomal mutations are the changes in the number and arrangement of genes in the chromosomes. The mutations occurring in the somatic chromosomes are called autosomal mutations.
These mutations can be either dominant or recessive. If even a mutation in one allele of the trait is expressed in the individual, it is called a dominant mutation but if the mutation is expressed only when both the alleles of the trait are mutated, then it is called autosomal recessive mutation.
In the given question, it is mentioned that both the parents have normal skin but their first child was an albino. So both the parents are the carriers for the disease. Their genotype must be Aa.
The cross between them can be represented as:
Parent generation- Aa X Aa
Cross-

| A| a
---|---|---
A| AA (Normal)| Aa (normal)
a| Aa (normal)| aa (albino)

As only in case of the genotype aa, the child will be suffering from albinism.
The probability of their second child being albino is= 1/4= 0.25
Therefore the percentage is 25%.
So, the correct answer is “Option B”.

Note: An autosomal recessive disorder is inherited only when the child inherits the recessive allele of the trait from both his parents. So his parents must either be affected by the disorder or carriers for it.