Question

Long answer question.

Explain the different factors responsible for genetic variations.

What is genetic variation? Explain any three factors responsible for genetic variation.

Answer 1

Definition: Genetic variations are caused due to various aspects of mutation, recombination, and migration. The change in gene and gene frequencies is known as genetic variation.

Genetic variations are caused by the following factors:

a. Gene Mutation:
Sudden permanent heritable change is called a mutation. Mutation can occur in the gene, in the chromosome, and in the chromosome number. The mutation that occurs within the single gene is called point mutation or gene mutation.
Mutation leads to the change in the phenotype of the organism, causing variation.

b. Genetic recombination:
In sexually reproducing organisms, during gamete formation, the exchange of genetic material occurs between non-sister chromatids of homologous chromosomes. This is called crossing over. It produces new genetic combinations that result in variations. Fertilization between opposite mating gametes leads to various recombinations resulting in the phenotypic variations causing a change in the frequencies of alleles.

c. Gene flow:
Gene flow is the movement of genes into or out of a population. Gene movement may be in the form of migration of organism, or gametes (dispersal of pollens) or segments of DNA (transformation). Gene flow also alters gene frequency causing evolutionary changes.

d. Genetic drift:
Any random fluctuation (alteration) in allele frequency, occurring in the natural population by pure chance, is called genetic drift.
e.g. When the size of a population is severely reduced due to natural disasters like earthquakes, floods, fires, etc., it causes the elimination of particular alleles from a population. Smaller populations have greater chances for genetic drift. It will result in a change in the gene frequency. Genetic drift is also an important factor for evolutionary change.

e. Chromosomal aberrations:
The structural and morphological change in chromosome due to rearrangement is called chromosomal aberrations. It changes the arrangement of the genes (order or sequence) that results in the variation.
Chromosomal aberrations occur due to the following reasons:

1. Deletion: Loss of genes from the chromosome.

2. Duplication: Genes are repeated or doubled in number on the chromosome.

3. Inversion: A particular segment of the chromosome is broken and gets reattached to the same chromosome in an inverted position due to 180° twists. There is no loss or gain of the gene complement of the chromosome.

4. Translocation: Transfer (transposition) of a part of a chromosome or a set of genes to a non-homologous chromosome is called translocation. It is affected naturally by the transposons present in the cell.

Chromosomal aberrations-