Mechanism of Organic Evolution

Estimated time: 5 minutes

Maharashtra State Board: Class 12

Key Points: Mechanism of Organic Evolution

Basic Processes - Evolution occurs in populations, not individuals; driven by mutations, recombination, gene flow, genetic drift, natural selection, isolation, and speciation.
Mutations & Recombination - Mutations - permanent heritable changes in genetic material; Recombination - new variations via crossing over, random gamete union, and anaphase separation.
Gene Flow & Genetic Drift - Gene flow - gene transfer between populations via migration; Genetic drift - random change in allele frequency by chance (Sewall Wright effect); greater effect in small populations.
Founder & Bottleneck Effect - Founder effect - a few individuals form a new population with different allele frequencies; Bottleneck effect - most of the population is wiped out by a disaster, and a few survivors rebuild.
Natural Selection Types - Stabilizing (favours intermediate; e.g. birth weight), Directional (eliminates one extreme; e.g. industrial melanism), Disruptive (eliminates intermediate; e.g. African finch beak sizes).
Isolation & Speciation - Isolation restricts gene flow via geographical barriers; over generations, isolated populations become so different that they form new species (speciation).