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Natural selection is unidirectional, while genetic drift is a random process. Here it is also important to note that genetic drift differs from natural selection. Thus, genetic drift is involved in determining genotypic variation in a population. Genetic drift fixes certain alleles while eliminating others.
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Thus, through each generation, the frequency of an allele is an outcome of a random process of gamete sampling by a process known as genetic drift. In a population, each individual produces multiple gametes however, only a few succeed in developing into adults. In such a situation process of natural selection is not applicable. Now consider a situation wherein the fitness of all genotypes is the same or neutral mutation, and all have an equal probability of passing through the natural selection. Interestingly, certain mutations are beneficial only when present in heterozygous and not in homozygous such mutations occur in a population in intermediate frequency by a process known as balancing selection. On the contrary, harmful mutations, i.e., mutations that reduce the carrier’s fitness, gradually disappear from the population by a process known as negative or purifying selection. This process of evolution is referred to as positive or directional selection. Mutations that confer higher fitness are naturally selected, and their frequency increases until they are fixed by replacing the ancestral population alleles. The process of natural selection that selects the fittest also plays a significant role in the fate of the mutations. Variations in the frequency of alleles within populations over time.Mutation-induced genetic variability that is continuously generated within populations.Two processes determine the evolution of living organisms: The neutral mutation hypothesis for evolution helps to understand the fundamental evolutionary question of how genetic variations are created in the life-history traits and are preserved in a population, even though natural selection is underway. As per the neutral theory, molecular diversity in a species is attributed to neutral mutations. This theory gave equal fitness to all the genotypes and had an equal likelihood to pass onto the next generation irrespective of its allele type. However, Darwin mentioned that neutral mutations result in genetic variation and neutral traits, which eventually get fixed in a species.Ī century later, population geneticist Motoo Kimura proposed evolution’s ‘ neutral theory‘. Accordingly, the mutations that have a beneficial effect only survive the process of natural selection. Neutral mutations also form the basis of the neutral theory of molecular evolution and the molecular clock.ĭarwin proposed the theory of evolution wherein only the fittest survives the process of natural selection.
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Interestingly, most mutations are neutral mutations. Thus these mutations have been termed neutral mutations. However, they have no phenotypic expression of these changes and do not alter the ability to survive and reproduce. However, besides these harmful and beneficial mutations, there are a number of mutations that contribute to the variations in the genetic makeup of the individuals. Accordingly, mutation can be deemed beneficial or harmful, and this also forms the basis of survival of the fittest.īeneficial mutations are transferred to the next progeny as they become essential for survival. Genetic alteration in these traits critically determines the adaptability of an organism to its new environment. Lifetime reproductive success, fecundity, longevity, viability, etc., are some of the life-history traits that determine the fitness of the genotype. Genealogies or phylogenies are built or marked based on these neutral mutations. Since these mutations can escape the process of natural selection, these mutations accumulate and add to the variations in the genetic pool or the genetic drift. In other words, fixation of the neutral mutations is independent of natural selection. To define as per population genetics, neutral mutations are the mutations whose spread remains unaffected by the process of natural selection.