The genotype of an individual with a dominant trait is not exactly known (A-). To establish the genotype, it is necessary to cross.

Since it is impossible to accurately judge the genotype by the phenotype (for example, a person with brown eyes by phenotype may have different genotypes: AA, or Aa), an analyzing crossing is used. It consists in the fact that the analyzed organism is crossed with an organism homozygous for a recessive trait – an analyzer. In accordance with the type of offspring, a conclusion is made about the genotype of the studied organism.

Let’s illustrate with an example with coat color.

Parents: AA (analyzed), aa (analyzer).

Offspring: Aa (dark color).

Parents: Aa (analyzed), aa (analyzer).

Offspring: Aa (dark color), aa (light color).

That is, if the studied individual is homozygous, all offspring will have a dark color, and if heterozygous, half of the offspring will have a dark color, and the other half will have a light color.

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