Question

What are the five factors that act to change allele frequencies?

Answer 1

Hint: According to Hardy-Weinberg equilibrium law, the relative frequency of alleles in the population remains constant from generation to generation in a population of sexually reproducing organisms when:
1. The population has to be large enough so that accidents of sampling may be ignored
2. Mating takes place at random
3. Mutation does not take place or if it does, the rate is the same in both directions and
4. All the members of the population survive and have equal reproduction rates.

Complete answer:
If there is any change in the frequency of alleles in a population it would indicate the evolutionary change.
There are five factors which affect the genetic equilibrium and induce the variability in the population. These factors are called evolutionary agents. These are:
1. Mutations
2. Recombination of genes
3. Gene migration or gene flow
4. Genetic drift
5. Natural selection.

1. Mutations:
- These are sudden, large and inheritance changes in the genetic material.
- Mutations are random and occur in all directions.
- Most Mutations are harmful or neutral.
- Rate of mutation is very low.
- Mutations create and maintain variations within a population,these also introduce new genes and alleles in a gene pool.
- Speciation may result from the accumulation of Mutations over a number of generations.

2. Recombination of genes:
- Recombination involves reshuffling of genes of chromosomes.
- Recombination chances are more in those organisms which undergo sexual reproduction and in those which involve gametogenesis followed by fertilization.
- Due to Recombination,though only reshuffling of already existing characters takes place and no new genes are produced, it leads to redistribution of different traits to different individuals of a population.
- Different combinations bring diversity in genotype and phenotype of different organisms. So Recombination is an agent which leads to evolution.

3. Gene drift:
It is the random change in the frequency of alleles occurring by chance fluctuations.

4. Gene migration (gene flow):
If two populations are genetically quite different, a small amount of immigration can result in large changes in allele frequencies. If the migrating individuals interact with the members of the local population, called hybridization, these may bring many new alleles into the local gene pool of the host population. This is called gene migration, So this addition or removal of alleles when individuals enter or leave a population from another locality is called gene flow.
When the gene flow is unrestricted then it decreases the differences between the gene pools and reduces the distinctiveness between different populations.

5. Natural selection:
The process by which comparatively better adapted individuals out of a heterogeneous population are favored by nature over the less adapted individuals is called natural selection.

Note:
The Hardy Weinberg principle acts as a tool which helps the population geneticists to determine the degree of evolutionary change by comparing allele frequencies at the starting point and at some future time. The amount of deviation between observed frequencies and those predicted by the Hardy Weinberg principle indicates evolutionary changes.