Mendelian Synthetic Theory of Evolution

The enrichment of Darwin’s theory by the perspectives of population genetics as well as the findings of paleontology and biogeography became what Julian Huxley called Modern Synthetic Theory of Evolution or Modern Theory of Evolution.

Most importantly this modern synthesis or modern theory is a recollection that is the populations that go through changes that are gradually affected by natural selection which acts on individuals.

The Modern (or Mendelian) Synthetic Theory of Evolution (additionally called Modern Synthesis) consolidates the idea of Darwinian development with Mendelian hereditary qualities, bringing about a brought-together hypothesis of advancement. This theory can also be called Neo-Darwin Theory and was presented by various transformative scholars like T. Dobzhansky.

Factors that Affect the Modern Synthetic Theory of Evolution

Stebbins discussed modern synthetic theory as well as the other factors which affect evolution in his book ‘Process of Organic Evolution.’

These factors are:

• Gene Mutation
• Chromosome structure and number change
• Natural selection
• Gene Recombination
• Natural selection
• Reproductive isolation
• Migration
• Hybridization
• Genetic drift
• Gene flow

Out of these factors responsible for evolution, gene mutation, natural selection and gene recombination are very important.

Gene Mutation

• Gene mutations include all the characters that are heritable that cause an alteration in the phenotype of a person.
• They include brand new genetic information by modifying some genes that are already available in a population.
• Many times genetic mutation happens for the first time but most times it might have already occurred earlier.
• The generation of all the alleles for a particular trait might have originated earlier in the past and thus are being preserved in the gene pool due to the result of sexual reproduction taking place within the species.
• If a harmful allele is produced due to mutation, it will be uncommon in the population.
• Usually, the mutations that occur are harmful and only some mutations can be regarded as valuable to the individual.

Gene Recombination

• Another vital process that is responsible for the generation of genetic variation is by the means of sexual reproduction.
• We know that sexual reproduction does not help in the generation of new gene information like mutation does, but it helps in the recombination of genes inside mixtures which was not possible earlier.
• The mixing up of genes at the time of sexual reproduction is referred to as genetic recombination.
• After sexual reproduction, the new individual produced will have genes that are in a complete set different from any other individuals who existed earlier.
• Recombination directly does not change the allele frequency within the gene pool but the new individual has a new set of genes that are unique which help them to carry out further reproduction.
• There happens an exchange of genetic material (like DNA) during meiosis by the non-sister chromatids that are brought crossing over. It prompts recombination and thus can be the reason for changes in the inheritance that are present inside a species.

Isolation

• It is one of the critical components answerable for the manufactured hypothesis of development.
• The isolation helps forestall the interbreeding of related living beings which is a regenerative type of recombination.

There are five types of isolation:

1. Geographical isolation
2. Reproductive isolation
3. Temporal or habitat isolation
4. Behavioural isolation
5. Mechanical isolation

Migration

• The migration of organisms from one place to another is also a very important aspect for the addition or subtraction of alleles from the population of a certain location or simply the local population.
• When any individual moves from one population and enters another one, the genetic information of the individual gets subtracted from the population it moved from and gets added to the population it gets attached to.
• If the individual possesses some rare alleles, it might also affect the allele frequency of both populations.
• Migration may or may not be great. As long as we have alleles leaving or entering a population, there will be a change in the gene pool.

Genetic Drift

• Genetic drift tells us about the changes in the frequency of a gene that cannot be subjected to selective pressures but happen because of the events which are unrelated to any inherited traits.

Natural Selection

• This is a type of mechanism that occurs at two intervals that are interrelated to one another, one at an organismic level and one at the allele level.
• It can be defined as the process through which the organisms that are better adapted to the environment physically, physiologically and behaviorally survive and those that fail to adapt themselves either die or are unable to reproduce further.

These topics are thoroughly discussed in NCERT Class 10 Science Chapter 9 Heredity and Evolution.