Question

4) Describe the four evolutionary mechanisms that alter the frequencies of existing genetic variation in natural populations. You need to define each mechanism and describe at least one example of its action in natural populations (e.g., genetic drift in overhunted populations resulting in less genetic diversity).

Answer 1

4.

Four evolutionary mechanisms that alter frequencies of existing genetic variation in natural populations

* Natural Selection

* Mutation

*Genetic Drift

* Gene Flow

* Natural Selection

Here nature selects the ones with desirable traits. It is the machine that drives evolution.It act on heritable traits acting in a population.The traits or phenotypes which are beneficial are selected and passed to next generations.  

The concept was developed by Charles Darwin . There are mainly three modes of natural selection ,

- Directional selection

- Stabilizing selection

- Disruptive selection

Industrial melanism, evolution of drug resistant HIV are evidences of natural selection. In industrial melanism , initially light coloured organism 's population become dark as a result of natural selection.

* Mutation

Mutations are a source of genetic variation. Mutations are result of change in DNA sequences. Mutations can be

- Beneficial

- Neutral

- Harmful

Benefical mutations can increase the reproductive fitness of the individual and thus fixed in the population. Mutations can be again divided as

- Germline Mutations

_ Somatic mutations

In the context of evolution germline mutations are important - seen in gametes and gets passed to next genertations. Somatic mutations are of less importance. Mutations are spontaneous in nature. They are random, non directional and non adaptive. E coli bacteria are able to mutate their genes in a directed way that enables cells to adapt the changing environmental conditions.

* Genetic Drift

The concept of genetic drift was proposed by Sewall Wright. The random change in allele frequencies as a result of chance due to sampling error from one generation to next in a finite population is called Genetic drift. It depends on population size. It is important in small populations.genetic drift is a random event.

examples

_ Population bottleneck

- Founder effect

Bottleneck effect occurs when a sharp decline in size of population due to environmental factors. Founder effect is yhe loss of variation when apopulation is seperated from larger one.

* Gene Flow

Gene flow is the flow of genes from one gene pool to another. It alters allele frequency of a population. Migrations are reason for this . Many factors influence the gene flow in the population.In the case of plants pollens help in gene flow.

example Sympatric and allopatric populations of Helioconius melpomene butterfly.