Microevolution

Microevolution is the gradual shift in allele frequencies within a population over time. This change occurs as a result of four distinct processes: mutation, natural and artificial selection, gene flow, and genetic drift. This change occurs over a relatively short period of time (in evolutionary terms) in comparison to the changes referred to as macroevolution.

Population genetics is the discipline of biology that establishes the mathematical framework for studying microevolution. Ecological genetics is concerned with the study of microevolution in the natural world. Typically, observable instances of evolution are microevolutionary in nature; for example, antibiotic-resistant bacterial strains.

Four Processes

Mutation

Mutations are flaws in the DNA sequence of a cell’s genome that are caused by radiation, viruses, transposons, and mutagenic agents, as well as meiosis or DNA replication errors. Errors are introduced most frequently during the replication of DNA, namely during the polymerization of the second strand. Additionally, these errors can be created by the organism itself through cellular mechanisms such as hypermutation. Mutations can alter an organism’s phenotype, particularly if they occur within the protein-coding sequence of a gene. Due to the proofreading capabilities of DNA polymerases, error rates are typically very low—one error every 10–100 million bases. (Without proofreading, error rates are a thousandfold higher; many viruses rely on DNA and RNA polymerases that are incapable of proofreading, resulting in increased mutation rates.) Mutagenic processes accelerate the pace of change in DNA: mutagenic substances cause errors in DNA replication, frequently by interfering with the base-pairing structure, whereas UV light generates mutations by causing damage to the DNA structure. Chemical damage to DNA happens naturally as well, and cells utilize DNA repair processes to correct mismatches and breaks in the DNA—however, the repair mechanism does not always successfully restore the DNA to its original sequence.

Mutation can result in a variety of distinct changes to DNA sequences; these changes can be insignificant, alter the product of a gene, or prohibit the gene from functioning. According to studies in the fly Drosophila melanogaster, if a mutation modifies a protein generated by a gene, the mutation is likely to be deleterious, with approximately 70% of these mutations being detrimental and the remainder being neutral or weakly beneficial. Due to the detrimental consequences that mutations can have on cells, animals have evolved techniques to remove mutations, such as DNA repair. Thus, the optimal mutation rate for a species is a trade-off between the expenses associated with a high mutation rate, such as harmful mutations, and the metabolic expenditures associated with sustaining mutation-reducing mechanisms, such as DNA repair enzymes. Viruses that employ RNA as their genetic material have a high mutation rate, which can work in their favour because these viruses will evolve continuously and fast, evading the defensive responses of the human immune system, for example.

Selection

Selection is the process through which heritable characteristics that increase an organism’s likelihood of survival and reproduction become more prevalent in a population over successive generations.

It is occasionally necessary to distinguish between naturally occurring selection, referred to as natural selection, and selection that is a result of human actions, referred to as artificial selection. This distinction is quite ambiguous. Nevertheless, natural selection is the primary mode of selection.

Natural genetic variation within a population of organisms ensures that some individuals will thrive in their current environment more than others. Factors affecting reproductive success are also significant, a point that Charles Darwin elaborated on in his theories of sexual selection.

Natural selection acts on an organism’s phenotype, or visible traits, but the genetic (heritable) underpinning of any phenotype conferring a reproductive advantage will grow more prevalent in a population (see allele frequency). This process can result in creatures becoming more specialised for particular ecological niches over time, and may finally result in speciation (the emergence of new species).

Genetic Drift

Genetic drift occurs when the relative frequency of occurrence of a gene variant (allele) in a population changes as a result of random sampling. That is, the offspring population’s alleles are a random sample of those in the parents. And chance plays a part in the survival and reproduction of an individual. The allele frequency of a population is the fraction or percentage of its gene copies that share a certain form relative to the total number of gene alleles that share that form.

Genetic drift is an evolutionary process that alters the frequency of alleles over time. It may result in the full erasure of gene variations, hence reducing genetic variety. In contrast to natural selection, which increases or decreases the frequency of gene variants based on their reproductive success, genetic drift changes are unrelated to environmental or adaptive forces and may be positive, neutral, or detrimental to reproductive success.

Gene Flow

The interchange of genes between populations, which are often of the same species, is referred to as gene flow. Within a species, gene flow occurs as a result of organisms migrating and then breeding, or as a result of pollen exchange. The generation of hybrid organisms and horizontal gene transfer are examples of gene transfer between species.

Migration into or out of a community has the potential to alter allele frequencies and introduce genetic variation. Immigration may contribute new genetic material to a population’s established gene pool. On the other hand, emigration may result in the loss of genetic material. Due to the fact that obstacles to reproduction between divergent populations are essential for the populations to evolve into new species, gene flow may hinder this process by spreading genetic differences between the populations. Mountain ranges, oceans, and deserts, as well as man-made constructions such as the Great Wall of China, all obstruct gene flow.

Macroevolution

Macroevolution refers to evolution at a level greater than the species level. It examines large-scale evolutionary changes, such as the origin of mammals and the evolution of flowering plants. Macroevolutionary studies rely heavily on fossil evidence. Understanding macroevolutionary changes enables us to comprehend the diversity of species and the rate at which they evolve across time.

Difference Between Microevolution and Macroevolution

Microevolution and macroevolution are two concepts that refer to the two scales at which organisms evolve.

Conclusion

Microevolution is a term that refers to the small-scale changes in gene frequency that occur within a collection of species that share a similar gene pool. This form of alteration occurs as a result of genetic material being recombined within a group of organisms. Thus, four factors contribute to this form of change: mutation, selection, gene flow, and genetic drift.