Hybrid Individual

A hybrid is the offspring of genetically different individuals. The term is used often to refer to the offspring of distantly related members of the same species or of closely related species. The potential production of fertile hybrids is a fundamental criterion to assign different individuals, strains, or races to a single biological species.

A heterozygote is an individual whose nuclei carry at least two different versions of at least part of the genetic information. The difference may consist in the nucleic acid sequence, the number of chromosomes, or the order of the genes in the chromosomes.

Mendelian Hybrid

 In a restricted sense, a Mendelian hybrid is the result of crossing two true-breeding strains)homozygotes).

A hybrid may involve two alleles A and a of a single gene (a monohybrid Aa), or two pairs of alleles at two different genes (the dihybrid AaBb), and so on. Hybrids produce characteristic Mendelian segregations in crosses with each other or with their parents.

 Genes that appear in heterozygosis in a polyhybrid may be carried in the same or different chromosomes. The dihybrid AaBb is said to be in the cis-configuration, or the coupling phase, when it contains two dominant alleles on the same chromosome and two recessive alleles on the homologous chromosome of the diploid; to make a graphic distinction, the genotypes of the homologous chromosomes are separated by a slash: AB/ab. The dihybrid AaBb is said to be in the trans-configuration, or the repulsion phase, when each chromosome carries a dominant and a recessive allele: Ab/aB. When two genes are sufficiently close in the same chromosome, their alleles do not form the random combinations expected from Mendelian inheritance; alleles in the same chromosome tend to remain together.

 Hybrids may be larger, more vigorous, or more resistant to adverse conditions than their parents. This phenomenon, called heterosis or hybrid vigor, occurs frequently in plants and animals and has led to the commercial production of hybrid seed for agriculture. Depending on the actual techniques that are used, hybrid seed may be too expensive and replaced in practical application by “double hybrid seed,” the offspring of two hybrids, each with different parents.