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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]
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.
A mule is a sterile hybrid of a male donkey and a female horse.Mules are smaller than horses but stronger than donkeys, making them useful as pack animals.. In biology, a hybrid is the offspring resulting from combining the qualities of two organisms of different varieties, subspecies, species or genera through sexual reproduction.
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 ...
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.
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.
Hybrid zones can form from secondary contact. A hybrid zone exists where the ranges of two interbreeding species or diverged intraspecific lineages meet and cross-fertilize. . Hybrid zones can form in situ due to the evolution of a new lineage [1] [page needed] but generally they result from secondary contact of the parental forms after a period of geographic isolation, which allowed their ...
The idea of a tree of life arose from ancient notions of a ladder-like progression from lower into higher forms of life (such as in the Great Chain of Being).Early representations of "branching" phylogenetic trees include a "paleontological chart" showing the geological relationships among plants and animals in the book Elementary Geology, by Edward Hitchcock (first edition: 1840).