Factors of evolution. Laboratory work 3

Evolution is the historical development of living organisms; its elementary form is the change of a population’s gene pool over generations. The factors that lead to evolutionary change are: 1) hereditary variation – mutations (the source of new alleles) and combinative variation (new combinations of alleles); mutations are random and non-directional, and many are kept hidden in the recessive state (in heterozygotes), forming a “reserve” of the population; 2) gene flow – exchange of alleles between populations by movement of individuals or gametes (seeds, pollen); 3) genetic drift – random change of allele frequencies in a small population; 4) population waves – periodic changes in number, after which the surviving individuals’ gene pool is a random sample; 5) isolation – geographic, ecological, biological and ethological; it stops gene exchange; 6) natural selection – the only directed factor: it raises the share of adapted genotypes in the population. The first four factors are random and non-directional, while selection gives directed change. Without hereditary variation selection has no material; without selection, changes do not lead to adaptation. So evolution results from the combined action of these factors. The sign that evolution is occurring in a population is that allele frequencies change from generation to generation. Darwin distinguished definite (group) and indefinite (individual) variation; for evolution the indefinite, i.e. hereditary, variation matters. Among genomic mutations, polyploidy is widespread in plants but rare in animals.