Evolution and Hardy Weinberg Principle

Mechanism of Evolution

Mechanism of Evolution explains the different ways and factors contributing to the process of evolution. Darwin explained evolution with the theory of natural selection according to which small variations lead to positive or negative adaptations which in turn lead to the evolution of a species. As Darwin was working on his theory of evolution, Mendel was pitching in the idea of genes as the inheritable character which brought about a change in the next generation. This discovery by Mendel was not taken into account by Darwin as a result of which he ignored the genetic changes that occurred during evolution.

Evolution

Hugo de Vries introduced the idea of gene mutations. These changes in the genetic structure give rise to phenotypic changes. He suggested that the sudden remarkable changes in the population were brought about by mutations. This mechanism contradicted Darwin’s theory of natural selection. Natural selection suggested variation which was minor and specific whereas, gene mutations were random and not specific. According to Darwin, evolution was a gradual and steady process but, de Vries introduced the concept of saltation – single step large mutations. It can now be easily seen that the theory of de Vries better accounts for the sudden massive extinctions from the planet and the level of speciation from a single ancestor species.

Hardy – Weinberg Principle

Hardy – Weinberg Principle mathematically explains the occurrence and consistency of gene frequency for a particular gene. The principle states that the allelic frequency remains constant through generations and the gene pool remains constant. This phenomenon is called genetic equilibrium. Also, all the allelic frequencies sum up to 1.

Let us assume, the frequency for the allele X in a population is a and that of the allele x is b.

Thus, the frequency of XX is a², xx is b² and Xx is 2ab. The equation can thus be represented as

a² + b² + 2ab = 1

or

 (a + b)² = 1

Factors affecting the Hardy-Weinberg principle:

• Mutation
• Genetic drift
• Natural selection
• Genetic recombination
• Gene flow

All these factors contribute to the change in gene frequency of a species in an area. If a few individuals from a species migrate to another place, the gene frequency changes again. It decreases from the place from where the individuals migrate and increase in the place they migrate to. If the frequency of the genes is high enough in the newly migrated land to start a new species, the migrated individuals become the founder species, and the effect is called the founder effect. Thus, all these mechanisms contribute to the process of evolution.

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