Hybridization

In biological science, hybrid has two significations. The first significance is the consequence of crossbreeding between two animals or plants of different taxonomic group. Hybrids between dissimilar species within the same genus are occasionally known as interspecies hybrids or crosses. Hybrids between different race within a species are called intra-specific hybrids. Hybrids between different genera are occasionally called intergeneric hybrids. Exceedingly uncommon interfamilial hybrids have been recognized to occur (such as the guinea fowl hybrids). The second type of hybrid comprises of crosses between populations, breeds or cultivars within a single species. This second meaning is frequently used in plant and animal breeding. In plant and animal engendering, hybrids are commonly produced and selected since they have suitable features not found or inconsistently present in the parent individuals or populations. This rearranging of the genetic material between populations or races is often called hybridization.

Interspecies hybrids are bred by mating two species, generally from inside the same genus. The offspring display traits and characteristics of both parents. The progeny of an interspecific cross oftentimes are sterile; thus, hybrid sterility prevents the movement of genes from one species to the other, keeping both species distinct. Sterility is often attributed to the different number of chromosomes the two species have, for instance donkeys have 62 chromosomes, whilst horses have 64 chromosomes, and mules and hinnies have 63 chromosomes.

While it is possible to predict the genetic composition of a backcross on average, it is not possible to accurately predict the composition of a particular backcrossed individual, due to random segregation of chromosomes. In a species with two pairs of chromosomes, a twice backcrossed individual would be predicted to contain 12.5% of one species’ genome (say, species A). However, it may, in fact, still be a 50% hybrid if the chromosomes from species A were lucky in two successive segregations, and meiotic crossovers happened near the telomeres.

Hybridization between two intimately related species is actually a basic occurrence in nature. Several hybrid zones are known where the ranges of two species meet, and hybrids are continually developed in avid numbers. These crossbreed zones are of value as biological model systems for analyzing the chemical mechanisms of speciation (Hybrid speciation). Recently DNA analysis of a bear shot by a hunter in the North West Territories confirmed the existence of naturally taking place and fertile polar bear/grizzly bear hybrids. There have been reports of similar supposed hybrids, but this is the first to be affirmed by DNA analysis. In 1943, Clara Helgason described a male bear shot by hunters during her childhood. It was large and off-white with hair all over its paws. The presence of hair on the bottom of the feet indicates it was a natural hybrid of Kodiak and Polar bear.

In some species, hybridization plays an important role in evolutionary biology. Whilst most hybrids are disadvantaged as a consequence of genetic incompatibility, the fittest survive, regardless of species boundaries. They may have a beneficial combination of traits allowing them to exploit new habitats or to succeed in a marginal habitat where the two parent species are disadvantaged. This has been seen in experiments on sunflower species. Unlike genetic mutation, which impacts only one gene, hybridization creates multiple variations across genes or gene combinations simultaneously. Successful hybrids could develop into new species within 50-60 generations. This leads some scientists to speculate that life is a genetic continuum rather than a series of self-contained species.

A number of conditions exist that limit the success of hybridization, the most perceptible is great genetic diversity between most species. But in animals and plants that are more closely related hybridization barriers include morphological differences, differing times of fertility, mating behaviors and cues, physiological rejection of sperm cells or the developing embryo.

Read more about Genetic Diseases and Dysmorphic Syndromes – Gaucher’s Disease