Question

A frameshift mutation could result from
A. A base insertion only.
B. A base deletion only.
C. A base substitution only.
D. Either an insertion or deletion of base.

Answer 1

Hint: Mutations are defined as sudden changes. They can be either spontaneous mutations or induced mutations. The chemicals that cause mutation are called mutagens. The examples of mutagens are nitrous acid, alkylating agents, base analogues, etc.

Complete answer:
> The smallest part of the gene that can undergo mutations is known as muton. In a DNA or RNA,
> Most of the gene mutations involve a change in only a single nucleotide or nitrogenous base of the cistron. These gene mutations are called point mutations. A mutation that involves more than one base pair is termed as gross mutation.
> Gene mutation may occur by three methods- inversion, substitution and frameshift.
> Inversion and substitution change one or few nitrogen bases without altering the reading of the subsequent bases. As a result one or few codons are changed. Due to substitution of bases transition or transversion occur.
> Insertion or deletion of one or more nucleotides of a cistron changes the reading of the frame of base sequence and causes frameshift or gibberish mutations. In this, an entirely new polypeptide is synthesized from the area of change.
> For example, in a type of thalassemia which is an inherited blood disorder resulting in anemia, the beta-chain of hemoglobin is changed due to frame shift mutation.
> Acridines are mutagens that cause frame shift mutation. They enter the DNA chains in between two base pairs and cause deletion or addition of a few nucleotides. The frame of the nucleotide sequence of DNA is disturbs and read differently.

So the correct answer is D. Either an insertion or deletion of base.

Note:
> Gene mutations usually occur during replication of DNA. It is therefore also called copy error mutation.
> Cancer which is uncontrolled cellular growth and divisions are often observed to be related to chromosomal mutations.