ABSTRACT
People know today that natural populations of all studied organisms are extremely variable at the molecular level. The chance that two individuals are genetically identical is practically zero, except in cases of asexually-reproducing organisms or identical twins. The source of all genetic variation are mutations and recombinations, which take place during DNA replication in the meiotic division and the union of gametes in fertilization. Mutations rarely occur, but recombination occurs frequently whenever the sexual cells divide. In the last two decades of the 20th century, the study of variable phenotypic expression of the same genotypes when exposed to different environments attracted much interest, both theoretical and experimental. From an evolutionary point of view, genetic heterogeneity and phenotypic plasticity are alternative strategies of a species to cope with variation in the environment. Phenotypic plasticity can be an adaptive strategy, pre-empting the need for genetic variation, – or it may be additional to genetic variation.
