Analyzing mating is the mating of a hybrid individual with an analyzer individual. As an analyzer, a homozygous individual is selected in which the recessive trait is reflected in the phenotype. Analytical crosses are widely used in breeding and genetics to determine the genotype.
As is known, according to the laws of genetics, a recessive trait in monohybrid crosses does not appear in the first generation. In the second generation, it appears only in one sixteenth of the individuals. The recessive trait is preserved in the genotype of individuals of the first generation, but does not appear externally in them. Thus, an individual of the first generation having a recessive trait in the genotype does not differ in phenotype from a monohybrid individual in the dominant trait. Analyzing crossing is aimed at obtaining information about the presence or absence of a recessive trait in the genotype.
Consider the mechanism for determining the genotype of an individual gray fly. Gray color is the dominant feature in relation to the black color of the body of the insect. A biologist crosses a gray fly with a black one and evaluates the resulting offspring. If all individuals have a gray color, then the studied fly had only a dominant trait in the genotype. If half of the resulting flies has a black color, then we can conclude that there is a recessive trait.
With incomplete dominance, each genotype has its own phenotype. In order to find out whether any trait observed in an individual is the result of incomplete dominance or an independent trait genetically incorporated, it is also necessary to carry out an analysis crossing. If the trait under investigation is the result of incomplete dominance, then its further “mixing” will occur with the recessive trait of the analyzer. If the trait was independent, then it will be transmitted unchanged to all individuals, if the studied individual is homozygous, or part of the individuals, if it is heterozygous. For example, if the pink and white flowers were crossed, they turned light pink, then there is an incomplete dominance. If all first-order hybrids have pink flowers, then this trait is embedded in the allele as an independent one and dominates white. In this case, the studied individual is homozygous. If part of the hybrids inherited the pink color of the petals, and the other part was transmitted white, then the pink trait is independent, dominant, the studied individual carries both traits in the genotype.
In practice, analyzing crosses is not always enough to determine the genotype. An example falling into the category of exceptions can be explained by one of three methods of non-allelic interaction of genes: epistasis, polymerization, or complementarity.
In epistasis, the manifestation of the genes of one allelic pair outside is suppressed by the genes of another allelic pair. Suppressors can carry both a dominant and a recessive trait. As a result of epistasis, when a homozygous individual with red flowers (dominant trait) is crossed with a homozygous individual with white flowers (recessive trait), only plants with red flowers will be in the first generation of hybrids, and 3/4 of hybrids will have a red color in the second generation, 3 / 16 is white, and 1/16 will inherit the trait of another allele (for example, yellow).
The following example can be given to explain the effect of the phenomenon of polymer. The flowers contain several heterozygous alleles that bear signs of red (dominant) and white (recessive) color of the petals. The more hybrid the second generation of recessive individuals, the whiter the flower. If an individual has alleles with or without a dominant trait, something in between something appears externally. When determining the genotype through analyzing crosses, the polymer is easily confused with incomplete dominance.
With complementarity, non-allelic genes complement each other and contribute to the formation of a new trait.