Modern theory of evolution: adaptive radiation: a cluster of closely related species that are each adaptively specialized to a specific habitat or food source, advanced characters: in current usage, approximately equivalent to personality. 10. autopolypoloidy: the genetic condition of having more than two sets of chromosomes from the same parent species. 11. behavioural isolation: a prezygotic reproductive isolating mechanism in which two species do not mate because of differences in courtship behaviour; also known as ethological isolation. 12. beneficial mutation: a change in the chemistry of a gene that is perpetuated in subsequent divisions of the cell in which it occurs; a change in the sequence of base pairs in the chromosomal molecule. 13. biological species: the definition of species based on the ability of populations to interbreed and produce fertile offspring. 14. bottleneck effect: drastic short-term reductions in population size caused by natural disasters, disease, or predators; can lead to random changes in the population"s gene pool.