Question

The mutation that involve addition, deletion or substitution of a single base pair in a gene are referred to as
(A) point mutation
(B) lethal mutation
(C) silent mutation
(D) retrogressive mutation

Answer 1

Mutation is usually defined as alterations in the DNA (Deoxyribose Nucleic Acid) sequences. Mutations could significantly occur as a consequence of mistakes made by DNA copying during the cellular divisions, contact made with the ionizing radiations or chemicals (mutagens), or infections occurred due to virus.

Complete answer:
Point mutation is a type of mutation which only influences a single nucleotide of the nucleic acid. Usually, the point mutation involves the substitution or addition of a single base for a different one that alters complementary bases in a DNA. Such types of mutations also involve deletions or insertions of a single base pair in a gene. Broadly, DNA mutations have been categorized into three types including base addition, deletion and insertion. For instance, the sickle-cell anemia is a type of disease which is caused due to a single point mutation within the beta-hemoglobin gene which alters the GAG codon into the GUG, leading to encoding of valine at the place of glutamic acid. In another case, if a fragment of a DNA molecule is not copied appropriately during the DNA replication, then it leads to deletion mutation. In point mutation, either the whole base pair gets missing or only the nitrogenous base present over the master strand may get missing. In case of point deletions, a single nucleotide gets deleted from the whole sequence.

Hence the correct answer is option ‘A’.

Note: Mutations occur instinctively at lower frequencies due to the chemical fluctuations of purine and pyrimidine base pairs and also due to the mistakes during the DNA replication.