Variation
மாறுபாடு
Do not confuse variation with mutation. Variation is the standard outcome of sexual reproduction, while mutation is a sudden, heritable change in DNA sequence. If you cannot distinguish between these two, you will lose marks on the very first page of this chapter.
The idea
Variation is the degree by which progeny differ from their parents. It is a key component of sexual reproduction and evolution.
Why it matters
It exists to provide the raw material for natural selection and evolution, allowing populations to adapt to changing environments.
NEET lens
Variation is the degree by which progeny differ from their parents. It is the fundamental driver of evolution and a mandatory consequence of sexual reproduction. NEET examiners test your understanding of how meiosis and fertilization generate this genetic diversity. Master this definition; it is the foundation for understanding Mendelian genetics.
Introduction
Variation is the degree by which progeny differ from their parents. It arises mainly through sexual reproduction and is the raw material for evolution.
Core concept
Sources of variation: (1) Recombination — crossing over between non-sister chromatids during prophase I of meiosis (pachytene) creates new gene combinations; (2) independent assortment of chromosomes during meiosis; (3) random fusion of gametes at fertilisation; (4) mutation — changes in DNA, the ultimate source of new alleles. In sexually reproducing populations, recombination is the most common mechanism of genetic variation. Asexual reproduction (vegetative reproduction, parthenogenesis, nucellar polyembryony) produces offspring that are largely identical to the parent.
Go deeper
Mutation creates new alleles, while recombination reshuffles existing alleles into new combinations. Natural selection acts on this variation; without it, populations could not adapt.
From Class 10
You and your siblings look alike but not identical — that difference is variation, caused by the mixing of genes from both parents.