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?
- 0.5
- 0.75
- 1
- 0.25
The Correct Option is D
Approach Solution - 1
Approach Solution -2
Chromosome mutations are changes in the number and organization of genes in the chromosomes, whereas genetic mutations are changes in the gene and its manifestations. Autosomal mutations are changes that take place in the somatic chromosomes.
These mutations might either be recessive or dominant. A dominant mutation is one that manifests in a person even if only one allele of the characteristic is altered; while, an autosomal recessive mutation is one that manifests in an individual only when both altered alleles of the trait are present.
The answer to the question is that although both parents have a fair complexion, their first kid was an albino. Hence, the sickness is carried by both parents. Their genetic makeup must be Aa.
The cross between them can be expressed as:
Parent generation- Aa X Aa
Cross-
| A | a | |
| A | AA (Normal) | Aa (normal) |
| a | Aa (normal) | aa (albino) |
Only in the case of 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 D”.
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Concepts Used:
Principles of Inheritance and Variation - Mutation
A Mutation is a change in the sequence of our DNA base pairs caused by numerous environmental stimuli such as UV light or mistakes during DNA replication. Germline mutations take place in the eggs and sperm and can be passed onto offspring, whereas somatic mutations take place in body cells and are not passed on.
Types of Mutations
There are three types of mutations, which are as follows:
Silent mutation
It refers to any change in DNA sequence that has no effect on the amino acid sequence in a protein or the functions that a protein performs. There is no phenotypic indication that a mutation has occurred.
Nonsense mutation
When there is a change in the sequence of base pairs due to a point mutation, that results in a stop codon. This leads to a protein that is either shortened or non-functional.
Missense mutation
A missense mutation occurs when a point mutation causes a change in the codon, which then codes for another amino acid.
The mutation is caused by the following factors:
Internal Causes
When DNA copies incorrectly, the majority of mutations occur. Evolution occurs as a result of all of these mutations. DNA makes a copy of itself during cell division. When a copy of DNA isn't flawless, it's called a mutation since it differs somewhat from the original DNA.
External Causes
When certain chemicals or radiations are used to break down DNA, it causes the DNA to break down. The thymine dimers are broken by UV radiation, resulting in altered DNA.