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Microbiology => Genetic Engineering => Hybrid
Hybrid
Hybrid, strictly defined, an offspring that is a cross between different species, genera, or, in rare cases, families. More loosely defined, a hybrid can also be a cross between parents of different subspecies or varieties of a species.
Hybrids occur in nature, where they serve the important evolutionary function of increasing genetic variety. They are also produced artificially by ensuring the meeting of sex cells from organisms of unlike types. The closer the parental relationship is, the more successful the hybrid. For example, parents differing only in a pigment trait, such as that determining flower or fur color, will usually produce a normal hybrid. Animals of two different species, however, usually produce sterile hybrids; thus, the male mule is the sterile offspring of a mare and a male donkey. Offspring of two different plant species are also usually sterile, but they can be reproduced by cuttings or grafting. Many sterile hybrid plants have been made fertile by chemical treatment, temperature change, and irradiation.
Hybrids often have what is called hybrid vigor; they tend to be larger, faster growing, and healthier than their parents. Thus, mules are bred for their strength, superior to that of either parent. Ornamental plants are bred for their larger flowers; nearly all corn and tomatoes grown today are hybrids that bear much larger fruit than their parental stock. Other plant hybrids of great importance in food production are wheat, rice, alfalfa, bananas, and sugar beets.
Evolutionary change in nature is often due to hybridization. Normally, different species are kept from hybridizing by such isolating mechanisms as mountains or different breeding seasons or courtship patterns. When these mechanisms break down, however, permitting crossbreeding between species, the number of different gene combinations is increased, as is the chance for a fertile hybrid to establish itself as a new species.
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