Question

Gene mutation is caused by
(a) Linkage
(b) Reproduction
(c) Changes in the sequence of chromosome
(d) Changes in the sequence of nitrogenous bases

Answer 1

Hint: Mutations are used to understand the relation between DNA and genes. This is because mutations affect the DNA which in turn affects the gene. This altered gene shows an abnormal phenotype that can be observed by us.

Complete answer:
The mutation is referred to as the phenomenon which results in the alteration of the DNA sequence of the genome. This alteration happens in the sequence of nitrogenous bases present.
The mutation in the DNA is of two types:
- Point mutation: In point mutation, a single base pair is replaced by another which causes a change in the amino acids produced during translation. A classic example of this is Sickle cell anemia. A single base- pair change in the gene that codes for the beta- globin chain of hemoglobin results in the production of valine instead of glutamine. This causes the red blood cells to change into sickle- shaped cells.
- Frameshift mutation: In this mutation, a base pair is either added or removed from the gene which causes a complete alteration of the reading frame starting from the point of mutation. However, if base pairs in the multiple of three are added or removed, this won’t affect the reading frame but there will be a change in the number of amino acids produced.

So, the correct option is ‘Changes in the sequence of nitrogenous bases’.

Additional information: The mutation is also seen in chromosomes where segments of genes are disturbed. These are called chromosomal aberrations or abnormalities and consist of the following types.
- Inversion: Part of the gene is inverted and attached again.
- Deletion: Part of the gene is deleted.
- Duplication: Part of the gene or the entire chromosome is duplicated.
- Translocation: Part of the gene from one chromosome is attached to a different chromosome.

Note: 

> Mutation and recombination cause change in the genetic material of an organism. This variation in DNA is what leads to evolution over time.
> Chromosomal aberrations are seen in cancer cells.
>The major cause of mutations is errors that happen during DNA replication and recombination.
> Mutagens are substances that induce mutation in the genome and include UV rays, chemotherapeutic drugs, etc.