Implications of Mutation in Evolution — 2019 Paper I

Approach

• Demand of Question: Explain mutation as a source of hereditary variation and assess its evolutionary consequences.
• Structuring the Response: Define mutation, distinguish its effects, and relate it to selection, drift, adaptation and speciation.
• Key Dimensions to Cover: Gene mutation, chromosomal mutation, genetic variation, natural selection, neutral mutations, deleterious mutations and evolutionary novelty.

Model Answer

Introduction: A mutation is a heritable change in genetic material. It is the ultimate source of new alleles and genetic variation, upon which natural selection, genetic drift and other evolutionary forces operate.

Evolutionary implications:

1. Source of new variation: Mutation introduces genetic variants not previously present in a population.

Mutation → New allele → Genetic variation → Evolutionary potential

1. Beneficial mutations: Some increase fitness under particular environmental conditions and may spread through positive natural selection.
2. Deleterious mutations: Many reduce survival or reproduction and are eliminated or maintained at low frequencies by purifying selection.
3. Neutral mutations: Mutations with little effect on fitness may change in frequency through genetic drift, especially in small populations.
4. Adaptive evolution: Mutations affecting physiology, immunity, metabolism or morphology may contribute to adaptation when environmental conditions change.
5. Genetic polymorphism: Mutation continually replenishes variation and may contribute to stable polymorphisms when combined with balancing selection.
6. Speciation: Accumulation of genetic differences between isolated populations can ultimately contribute to reproductive isolation.

Critical point: Mutation is random with respect to adaptive need; selection determines whether particular mutations increase or decrease in frequency.

Conclusion: Mutation supplies the raw material of evolution, while selection, drift and gene flow determine the evolutionary fate of the resulting variation.