Question

Explain why a recessive allele that causes disease may not be eliminated by natural selection.

Answer 1

Q) Natural selection is an evolutionary process in which individual organisms or phenotypes having favourable characters, which better suit to the environment they live are able to survive and reproduce in that particular environment.

Natural selection considers the phenotype of an organism. A character in an individual is controlled by two alleles of a particular gene, suppose a person has a dominant allele of a gene and a recessive allele of the same gene, than the dominant allele gets expressed and the recessive allele remains in a hiding condition, this happens in heterozygous condition, as a result the recessive allele can remain in the gene pool.

In heterozygous condition a recessive allele gets masked by a dominant allele, due to which the recessive allele which causes the disease may not be eliminated by natural selection. But at times when there are two recessive alleles of a particular gene which gets expressed, that is in homozygous condition there is a chance of elimination of that particular recessive allele if it is not favourable to the environment.

For example suppose for a disease there are two alleles Ww, in this case w allele causes the disease which is a recessive allele. The disease gets expressed when both the alleles are recessive that is in ww condition. But in heterozygous condition that is in Ww condition the recessive allele (w) remains in a hiding condition behind the dominant allele (W) and do not get expressed, being a carrier of the disease. Which can be transferred to the next generation, in this way the recessive allele remains in the gene pool, and it may not be eliminated by natural selection.