Hybrid Analysis

a method for studying the hereditary properties of an organism by crossing (hybridizing) it with a related form and then analyzing the traits of the progeny.

Hybrid analysis was first used by G. Mendel in 1865 to study the mechanism of transmission of hereditary factors (genes) from parents to progeny and to study the interaction of genes within the same organism. Hybrid analysis is based upon the capacity for recombination (the redistribution of genes in the formation of gametes), which results in new combinations of genes. One can judge the genotype of the parental form from these combinations, which show up in given proportions in the progeny of a hybrid individual; from the genotype of the parental form one can predict the genotype of the progeny. Thus, the genotype of an individual that is hybrid for a pair of alleles, one of which is the dominant A and the other the recessive a, can be represented as Aa. Externally, or phenotypically, such a form (heterozygote) is indistinguishable from a form with genotype AA(homozygote). A hybrid (Aa) forms two kinds of gametes, each of which carries either an A allele or an a allele; the gametes themselves are never hybrid. Using various kinds of crosses, one can find out how many types of gametes an organism forms for a given gene and determine its genotype. If self-fertilization (a frequent phenomenon in plants) is possible in the form being analyzed (Aa), it will look like this schematically: ♂(A + a) × ♀ (A + a) → AA + Aa + Aa + aa. A new form, aa, will appear in the progeny with a given frequency.

If there is no self-fertilization, the genotype of the parental form will be revealed by crossing its progeny in various combinations (brother × sister) and analyzing the “grandchild” generation. Another method of revealing hybridity is through the test cross—that is, by crossing the presumed hybrid with the recessive parental form. Hybrid analysis plays an important role in selection and breeding because it can be used to determine cases of identity of phenotype and genotype. Hybrid analysis is applied here in analyzing the stock by the progeny in order to detect hidden undesirable genes in the stock. It is also used in drawing up chromosome maps. A knowledge of the genetic composition of a chromosome permits the introduction of a particular chromosome or group of genes into the genome through special crosses in order to create forms with the desired genotype. This method is widely used in horticulture. Hybrid analysis is used to study the interaction of genes in the first hybrid generation (complementarity test). Hybrid analysis is the principal method of genetic analysis.