Studies gene frequencies and how genes are distributed in natural populations; of course, it is also interested in the causes (mutation, selection, etc.) that determine variations in the frequencies themselves. One of the main purposes of population genetics is to elucidate the evolutionary mechanisms and evolutionary prospects of a population, since biological evolution is ultimately linked precisely to changes in gene frequencies. By identifying gene frequency variabilities within a natural population, population genetics studies groups of individuals (populations) that stand between the individual and the species as it believes they constitute the basic unit in which all evolutionary processes occur, or at least all those essential to the transformations of one species into one or more others.
Analyses of variations in the gene structure of populations are carried out, today, not only by direct investigations within a population, but also by simulating with mathematical models what takes place in an ideal population, namely, an infinitely large population in which all individuals have an equal probability of mating, as well as even in the absence of mutation and selection. In such a population, equilibrium of genotype frequencies is established within a generation, whatever the initial gene frequencies were. Based on this model, it can be established that genetic equilibrium is achieved, i.e., a new species occurs, when frequencies remain unchanged in subsequent generations.
Another of the most topical problems in population genetics is the study of the causes of variations in gene frequencies among populations. There are two theoretical positions in this regard: the panselectionist and the panneutralist. According to the former, differences in allele frequencies are due to natural selection in that only certain alleles are more or less advantageous in a suitable environment for that population.
An example of this is the gene for thalassemia that is frequent in populations in areas where malaria is prevalent and protects heterozygous carriers from the onset of this disease. The second, panneutralist hypothesis considers genes to be selectively neutral and variations in frequency in populations due to random factors. One example is the fact that many electrophoretic variants of proteins show no changes in functional properties, such that it is likely that there are selectively neutral or near-neutral alleles. However, there is no firm evidence to date in favor of either hypothesis. The significance to be attributed to this genetic variability in populations is the main point of discussion among various currents of evolutionary scholars.
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