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Introduction to Population Evolution

A population, also known as a species, is a group of individuals who can all interbreed. The collection of these genes is known as a gene pool because these individuals can share genes and pass on combinations of genes to the next generation. Only populations, not individuals, go through the evolutionary process. Evolution is the means of transforming the gene frequencies within a gene pool; a single individual cannot evolve on their own. Mutations, natural selection, genetic drift, genetic hitchhiking, and gene flow are five forces that can trigger genetic variation and evolution in a population.

Definition of Evolution in Population Genetics

The frequency at which a particular allele happens in a population is known as allele frequency (or gene frequency). A change in the frequency of an allele in a population is characterized as an evolution in population genetics.

Genetic Variation: Five Forces

Mutations

Why are some organisms able to live while others perish? These organisms that have survived have traits or characteristics that provide them with advantages. A mutation, or a change in the genetic code, is responsible for each of these characteristics. Mutations happen naturally, but not all of them are heritable; mutations in gametes are only passed down to offspring if they occur in the gametes. These heritable mutations are what cause new traits to emerge in a population.

Natural Selection

Natural selection behaves on the frequency of those traits in the same way that mutations cause new traits in a population. Because there are more organisms than resources, every organism is constantly fighting for survival. Individuals with superior traits will be capable of producing more offspring as a result of natural selection. The higher an organism’s fitness, the more offspring it can create. Natural selection perpetuates the traits that confer a benefit as new traits and behaviors emerge as a result of mutation.

Genetic Drift

Gene frequencies prefer to “drift” due to random events when selective forces are missing or relatively weak. This drift comes to a halt when the gene variation becomes “fixed,” either by vanishing from the population or by completely replacing the other variations. Even when selective forces are absent, genetic drift can result in two distinct populations with the same genetic structure drifting apart into two divergent populations.

Genetic Hitchhiking

When recombination takes place during sexual reproduction, genes are typically shuffled so that each parent passes on a random assortment of genetic variations to their offspring. Genes that are close together on the same chromosome, on the other hand, are frequently assorted together. As a result, if a gene’s proximal genes impart a benefit, its frequency may boost a population through genetic hitchhiking.

Gene Flow

The exchange of genes between populations or species is known as gene flow. When the gene pools of two populations differ, the exchange of genes can result in variation that is beneficial or harmful to one of the populations. If this gene variation is advantageous, it may eventually replace all other variations, resulting in the entire population exhibiting that trait.

DNA Sequencing and Comparative Genomics

A DNA segment, a whole-genome, or a complex microbiome can be sequenced to reveal the genetic information contained within it. Scientists can deduce which genes and regulatory instructions are contained in a DNA molecule using sequence information. Gene-specific features such as open reading frames (ORFs) and CpG islands can be screened in the DNA sequence. For evolutionary analysis between species or populations, homologous DNA sequences from different organisms can be contrasted.

Comparative genomics is a branch of biology that compares the genome sequences of different species, including humans, mice, and a wide range of other organisms from bacteria to chimps. Researchers can learn what distinguishes different life forms at the molecular level by comparing the sequences of genomes from different organisms. Comparative genomics is also a useful tool for studying evolutionary changes in organisms, as it can help identify genes that are conserved or shared across species, as well as genes that give each organism its own distinct characteristics.

References:

  1. Iwasaki WM, Kijima TE, Innan H. Population Genetics and Molecular Evolution of DNA Sequences in Transposable Elements. II. Accumulation of Variation and Evolution of a New Subfamily. Molecular biology and evolution. 2020 Feb 1;37(2).
  2. Parks M, Subramanian S, Baroni C, et al. Ancient population genomics and the study of evolution. Philosophical Transactions of the Royal Society B: Biological Sciences. 2015 Jan 19;370(1660).

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