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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]
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 ...
For example, when trait combinations lead to reduced fitness in the hybrid offspring in specific environments. Genome stabilization - the process by which different ancestry blocks or introgression tracts become fixed within a hybrid species when hybridization between the hybrid taxon and its parent taxa has ceased.
Hybridization is considered to be an evolutionary catalyst capable of generating novel genotypes or phenotypes in a single generation. [1] [2] It can also happen with morphologically dissimilar but closely related species (Example: Helianthus giganteus, the giant sunflower). [4]
These masterful studies provided concrete support for the theory of natural selection, at the same time illustrating the fruitfulness of combining field and laboratory work in the study of evolution. [17] Adaptive evolution occurs through the dominance and survival of competing genes within a species.
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.
While some degree of gene flow occurs in the course of normal evolution, hybridization with or without introgression may threaten a rare species' existence. [20] [21] For example, the Mallard is an abundant species of duck that interbreeds readily with a wide range of other ducks and poses a threat to the integrity of some species.
Adaptationism is an approach to studying the evolution of form and function. It attempts to frame the existence and persistence of traits, assuming that each of them arose independently and improved the reproductive success of the organism's ancestors.