Hybrid

A hybrid is the offspring produced by organisms of two different varieties or species. Hybridization occurs often in nature between different varieties of the same species, but much less often between related or different species. The product of such a cross is usually unable to reproduce itself.

A hybrid is basically the product of two different organisms. In the plant kingdom, hybrids occur all the time both by natural pollination and when humans deliberately cross different types. Wheat is a hybrid that came about naturally, although the types grown now are hybridized even further by farmers so they will resist certain diseases and produce higher yields. Probably the most famous hybridizer was the Austrian monk and botanist (a person specializing in the study of plants) Gregor Johann Mendel (1822–1884), whose famous experiments with garden peas led to his discovery of the laws of heredity. Mendel spent years deliberately crossing different varieties within a species to produce other new varieties. Mendel started by crossing plants that bred different true traits (such as all tall or all dwarf), and produced hybrid plants whose varied offspring eventually led him to discover the phenomena he called dominant and recessive traits. Today, different types of plants are crossbred by farmers to produce a particular combination of desirable features.

In the animal world, a hybrid is more of an exception. Nature seems to work against members of different species trying to mate and reproduce, and if fertilization does somehow occur, the result is usually not able to survive much past birth. Very often, the fertilized egg does not develop properly and it dies. In instances where the two animals are members of different but closely related species, the offspring is born but it is usually sterile or unable to reproduce. The best-known animal hybrid is probably the mule. In this case, two closely related species, the horse and the donkey, are able to mate and produce an offspring. However, because the horse has sixty-two chromosomes and the donkey has sixty-four, the hybrid mule is born with sixty-three. It is therefore unable to successfully fertilize another animal because its odd-numbered chromosomes are unable to pair up correctly during meiosis (the special form of cell division that produces sex cells). A mule is a cross between a female horse and a male donkey. A "hinny" (also sterile) is the result of a male horse mating with a female donkey. While both mules and hinnies can be healthy, vigorous animals, they are nonetheless unable to reproduce because of what is called hybrid infertility. As a result, self-sustaining mule or hinny population could never develop since both must necessarily be produced by repeating the original crossbreeding.

[See alsoFertilization; Genetics ]

Hybrid

A hybrid is an offspring between two different species, or the offspring between two parents of the same species that differ in one or more heritable characteristics. An example of the first kind of hybrid is a mule, a cross between a female horse (Equus caballus ) and a male donkey (E. asinus ). An example of the second kind is the offspring from a cross between true-breeding red- and white-flowered garden peas (Pisum sativum ).

Hybrids between species are often sterile because they fail to produce viable reproductive cells that is, eggs, sperm, or spores. These cells develop improperly because the chromosomes from one species do not pair correctly during meiosis with the chromosomes from the other species.

Despite their sterility, hybrids may thrive and expand their ranges by reproducing asexually. For example, in the eastern United States and adjacent Canada, there are hundreds of distinctive hybrids of hawthorn (Crataegus ) and blackberry (Rubus ) that are not interfertile. Yet these hybrids may be common because they are able to set seed from asexually produced embryos, a special form of propagation called apomixis (Greek apo, away from, and mixis, mix, union—referring to the lack of fertilization). Also, in blackberries, the first-year stems are able to root at the tip, a form of propagation called vegetative reproduction.

Some hybrids become fertile by doubling their chromosome number, a process called polyploidy. Hybridization followed by polyploidy has been extremely important in plantevolution, especially among ferns and grasses. Examples are the wheats used to make bread and pastas, and species of wood fern (Dryopteris ) and spleenworts (Asplenium ).

Hybrids are generally infrequent in nature. Nevertheless, once formed they may be important for evolution because of the way they combine the characteristics of their parents. Especially in changing or disturbed habitats, hybrids that contain new genetic combinations may be better adapted to the new environments than either of the parents. Thus they may be able to colonize new habitats where neither parent can grow.

See also Asexual reproduction; Genetics.

Hybrid

A hybrid is an offspring between two different species , or the offspring between two parents of the same species that differ in one or more heritable characteristics. An example of the first kind of hybrid is a mule, a cross between a female horse (Equus caballus) and a male donkey (E. asinus). An example of the second kind is the offspring from a cross between true-breeding redand white-flowered garden peas (Pisum sativum).

Hybrids between species are often sterile because they fail to produce viable reproductive cells that is, eggs, sperm, or spores. These cells develop improperly because the chromosomes from one species do not pair correctly during meiosis with the chromosomes from the other species.

Despite their sterility, hybrids may thrive and expand their ranges by reproducing asexually. For example, in the eastern United States and adjacent Canada, there are hundreds of distinctive hybrids of hawthorn (Crataegus) and blackberry (Rubus) that are not inter-fertile. Yet these hybrids may be common because they are able to set seed from asexually produced embryos, a special form of propagation called apomixis (Greek apo, away from, and mixis, mix, union—referring to the lack of fertilization ). Also, in blackberries, the first-year stems are able to root at the tip, a form of propagation called vegetative reproduction.

Some hybrids become fertile by doubling their chromosome number, a process called polyploidy. Hybridization followed by polyploidy has been extremely important in plant evolution, especially among ferns and grasses . Examples are the wheats used to make bread and pastas, and species of wood fern (Dryopteris) and spleenworts (Asplenium).

Hybrids are generally infrequent in nature. Nevertheless, once formed they may be important for evolution because of the way they combine the characteristics of their parents. Especially in changing or disturbed habitats, hybrids that contain new genetic combinations may be better adapted to the new environments than either of the parents. Thus they may be able to colonize new habitats where neither parent can grow.

See also Asexual reproduction; Genetics.

hy·brid / ˈhīˌbrid/ • n. a thing made by combining two different elements; a mixture: the final text is a hybrid of the stage play and the film. ∎  Biol. the offspring of two plants or animals of different species or varieties, such as a mule (a hybrid of a donkey and a horse): a hybrid of wheat and rye. ∎ offens. a person of mixed racial or cultural origin. ∎  a word formed from elements taken from different languages, for example television (tele- from Greek, vision from Latin). ∎  a hybrid car.• adj. of mixed character; composed of mixed parts: Mexico's hybrid postconquest culture. ∎  bred as a hybrid from different species or varieties: a hybrid variety hybrid offspring.DERIVATIVES: hy·brid·ism / ˈhībrəˌdizəm/ n.hy·brid·i·ty / hīˈbriditē/ n.

hybrid
1. An individual plant or animal resulting from a cross between parents of differing genotypes. Strictly, most individuals in an outbreeding population are hybrids, but the term is more usually reserved for cases in which the parents are individuals whose genomes are sufficiently distinct for them to be recognized as different species or subspecies. A good example is Spartina town-sendii, produced by cross-breeding Spartina maritima (British cord grass) and the North American species Spartina alterniflora (each of which can breed true as a species). Hybrids may be fertile or sterile depending on qualitative and/or quantitative differences in the genomes of the two parents. Hybrids like Spartina townsendii, whose parents are of different species, are sterile, but generally reproduce vegetatively.

2. By analogy with (1), any heterozygote. Each heterozygote represents dissimilar alleles at a given locus, and this difference results from a cross between parental gametes possessing differing alleles at that locus.

3. (graft hybrid) see GRAFT.