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Introgression is an important source of genetic variation in natural populations and may contribute to adaptation and even adaptive radiation. [7] It can occur across hybrid zones due to chance, selection or hybrid zone movement. [8]
Rapid sympatric speciation can take place through polyploidy, such as by doubling of chromosome number; the result is progeny which are immediately reproductively isolated from the parent population. New species can also be created through hybridization, followed by reproductive isolation, if the hybrid is favoured by natural selection.
Eukaryote hybrid genomes result from interspecific hybridization, where closely related species mate and produce offspring with admixed genomes.The advent of large-scale genomic sequencing has shown that hybridization is common, and that it may represent an important source of novel variation.
Hybridization without change in chromosome number is called homoploid hybrid speciation. [1] This is the situation found in most animal hybrids. For a hybrid to be viable, the chromosomes of the two organisms will have to be very similar, i.e., the parent species must be closely related, or else the difference in chromosome arrangement will ...
There is some evidence of adaptive evolution in genes linked to brain development, but some of these genes are often associated with diseases, e.g. microcephaly (see Table 2). However, there is a particular interest in the search for adaptive evolution in brain genes, despite the ethical issues surrounding such research.
Because hybridization is costly (e.g. giving birth and raising a weak offspring), natural selection favors strong isolation mechanisms that can avoid such outcome, such as assortative mating. [5] Evidence for speciation by reinforcement has been accumulating since the 1990s.
This is due to adaptive radiation, or the evolution of varying traits in light of competition for resources. Gene flow moves in the direction of what resources are abundant at a given time. [37] Island Population: The marine iguana is an endemic species of the Galapagos Islands, but it evolved from a mainland ancestor of land iguana. Due to ...
However certain natural constraints act to limit the evolution of inbreeding avoidance, particularly when there is a risk of mating with a partner of a different species (heterospecific mating) and losing fitness through hybridization. [16] Inclusive fitness appears to be maximized in matings of intermediately related individuals. [17]