Hybrid is the offspring of two parents that belong to different species, stock, races, or breeds. For example, the mule is a hybrid of two different species, a jackass (male donkey) and a mare (female horse). Sometimes parents of hybrids differ only slightly. Hybrid corn is produced by parent plants that may differ in only a few traits. Hybrids whose parents are very different may be sterile (unable to reproduce). The mule is one of these.
Scientists have found that hybrids occur naturally. Natural hybridization is important, because offspring of different capabilities are produced. Many of them die. But some grow and develop well under conditions unfavorable to the parents, and they may start a new species.
Each parent of a hybrid has a different set of genes, which are passed on to the offspring during reproduction. Sometimes certain hybrids are called mongrels.
Hybrid Plants. Man can develop a new type of plant quickly with hybridization. The best hybrids may be superior to the parents in yield, hardiness, quality, or resistance to disease. For example, the cultivated strawberry is a hybrid that has larger fruit and better flavor than its wild parents. Certain hybrid tomatoes may contain more vitamins than either parent. Hybrid corn produces higher yields, and it also may withstand drought and disease better than regular varieties. American growers have produced many hybrids of citrus fruits. They crossed the orange and lemon to produce the oramon. By crossbreeding the grapefruit and lemon, they produced the lemelo. Crossbreeding the trifoliate orange and sweet orange produced the citrange. These hybrids can be produced without seeds bygrafting (uniting parts of two different kinds of plants).
Hybridization in plants was not recognized as early as in animals, because men did not understand how plants reproduced. Ancient peoples knew that date palm trees would not produce fruit unless the flowers of the fruit-bearing palm were dusted with pollen from those trees that did not bear fruit. But they did not know why this was so. In 1694, a German professor, Rudolfjakob Camerarius(1665-1721), proved that plants reproduce sexually. He showed that no seed would form on corn plants unless pollen from the tassel was applied to the silks of the ear. People then became interested in plant hybrids. But they did not begin to understand hybridization until the early 1900's when scientists rediscovered Gregor Mendel's work in plant heredity and developed his theories.
Hybrid Animals. Hybridization is usually more successful in plants than in animals because most controlled plant crosses are easier to make. But many valuable hybrid animals, or animals of hybrid origin, have been produced. Among these is the cattalo, which was developed from domestic cattle and the American buffalo. Animal breeders in the southern United States have also crossbred domestic cattle with the Brahman cattle of India and with the Afrikanders of Africa. In this way, they developed breeds that can endure heat and humidity and resist tropical diseases. Hybridization makes it possible to produce pigs with more lean meat and less fat, and chickens that produce more meat or eggs but eat less feed.
Animal hybridization is limited because the more parents differ from one another, the more difficult it is to produce offspring. Some animals may be unable to mate. In some species, the embryo produced cannot develop fully, because the genes of the parents cannot function normally.
