Question

The reason why some mutations which are harmful and yet do not get eliminated from gene pool is that
(A) They have future survival value.
(B) They are recessive and carried by heterozygous individuals.
(C) They are dominant and show up more frequently.
(D) Genetic drift occurs because of a small population.

Answer 1

Mutations refer to the alteration of the nucleotide sequence in the genome of an organism. Mutations lead to abnormal protein synthesis which leads to several abnormalities and genetic diseases. Some mutations are not inheritable whereas several are inherited over generations.

Complete answer:
To answer this question, we must know about the characteristics or significance of mutation.
i) Mutation is the change in the nucleotide sequence due to internal or external factors.
ii) Mutations lead to evolution of new species due to accumulation of mutations over time.
iii) Organisms undergo mutations which leads to the change in genotypic and phenotypic variations.
iv) The significant dominant mutations which are beneficial are carried over generations to generations whereas the once which are harmful is discarded through natural selection. (Option C is incorrect)

Certain mutations are recessive and do not cause any change in the phenotype. These are called silent mutations and are carried over generations through heterozygous individuals. They can only express themselves when they are homozygous recessive. Thus, they exist in the gene pool and cause abnormalities even after several generations.

The alteration in the occurrence of a gene in a smaller population, although it is unable to preserve them but brings about transformations, is referred as genetic drift. (Option D is incorrect)

Thus, the correct answer is option ‘B’.

Note: In genetic studies various types of mutagens are reported which can cause mutations. This mutagen includes radiations from different sources such as X-rays, alpha particles, gamma rays, ultra violet. Few chemical agents could harm the DNA (Deoxyribose Nucleic Acid) molecules and thus cause mutations. Cancer is a result of harmful mutation in which the cells start dividing abnormally.