Genetics - A. V. Sivolob 2008

Population genetics

The sexual process (the rudiments of which are manifested even in prokaryotes, see Chapter 5) creates conditions for Gene exchange between individuals of the same species inhabiting a common territory. It is precisely such a group of individuals sharing a specific gene pool—a population—that serves as the elementary unit of the evolutionary process.

A population is defined as a group of individuals of the same species sharing a common range (inhabiting a shared territory) and a common gene pool separated from neighboring groups (Fig. 8.1). Close genetic relationships are established among the individuals of a population, manifested as more or less free interbreeding within the group. Separation from adjacent populations occurs due to a certain limitation of these interactions with other groups (isolation from other populations). Evolutionary changes in a species occur through alterations in the gene pool—the total aggregate of genes—of each such population.

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Fig. 8.1. A population of Adélie penguins on the Yalour Islands (Argentina Range archipelago, Antarctica) consists of separate colonies and exhibits a characteristic "insular" Spatial Structure. One of such colonies is shown in the foreground.

A population is not merely an arithmetic sum of individuals; rather, it is a complex system possessing specific Structural and functional features. The characteristics of a population as a system are based on the species and individual traits of its constituent organisms, yet they cannot be reduced to the mere sum of these traits. Conversely, The properties of the organisms comprising a population depend on the features of that population and are shaped under the conditions of its existence. Therefore, Population Genetics—the subject of which encompasses the genetic parameters of groups of individuals and the dynamics of these parameters—is characterized by specific problematics and Research Methods.

The most important parameters characterizing a population include Abundance, Variability, structure, and reproductive characteristics (Mating Systems), as well as gene (allele) and genotype frequencies. Together with other factors, these parameters determine the uniqueness of a population's gene pool and its genetic structure.