Xenogamy
Xenogamy (also called outbreeding) is a term used to describe the union of genetically unrelated organisms within the same species. Xenogamy promotes genetic variability and vitality within a breeding population by eliminating homozygous individuals. Accordingly, with dominance, lethal or deleterious alleles have a better chance of being repressed by the dominant alleles in heterozygous organisms, thus reducing the impact of lethal or deleterious alleles within a population.
Xenogamy, or outbreeding promotes genetic diversity and thus, also enhances the overall fitness of a species. By producing new and varied combinations, outbreeding is a fundamental part of natural selection and an essential element of evolution. As such, outbreeding is an important tool in the continued survival and evolution of a species.
In plant species, there are several natural mechanisms that can result in xenogamy, including self-incompatibility. With self-incompatibility, there is an inability on the part of sex cells (gametes) from the same species of plants to produce a viable embryo. With such species, it is usually the case that pollen, unable to induce fertilization on its own style, is able to successfully grow down the style of other plants of the same species. The process involving the transfer of pollen to a foreign stigma is termed allogamy. Regardless of the exact mechanism, self-incompatibility mechanisms promote xenogamy (outcrossing) and heterozygosity while acting to prevent inbreeding. Self-incompatibity is often the result of incomplete nuclear or genetic fusion. The failure of the fusion processes are usually traced to a single genetic locus (S locus) that exists as multiple alleles.
In some circumstances, xenogamy and outbreeding are also referred to as cross breeding. Regardless of the exact terminology, the core concept involves an increase in genetic variability. Such increases in genetic variability exert measurable influences on the frequency of genes, types of alleles, and traits within a population.
With crossbreeding, genetically dissimilar or unrelated animals from the same breed can be crossed in a process known as outcrossing. True crossbreeding exists when, for example, differing breeds of cattle are allowed to mate and produce offspring. Extreme xenogamy exists with species crossing (a mating between organisms from two different species).
Xenogamy or crossbreeding is often the attempt by scientists to genetically combine desirable traits to form two differing species or breeds in order to produce offspring with more desirable characteristics. Successful crossbreeding, whether in plants or animals, usually results in increased hybrid vigor (heterosis). Hybrid vigor refers to a mating system criteria that measure the better than normal growth rates, immunological tolerance, strength, and other desired characteristics of a hybrid species.
In contrast to xenogamy or allogamy there are the processes of inbreeding and autogamy (self-pollination).
This is the complete article, containing 433 words
(approx. 1 page at 300 words per page).
