单杂交组合

Using the pea plant Gregor Mendel originally performed monohybrid crosses. Breeding experiments between organisms that vary by a single trait like pod color.

For example, in the original parental generation, P zero, one parent has all green pods. It's genotype is homozygous for the green pod color allele represented as upper case G's . The other parent has only yellow pods and is homozygous for the yellow pod allele indicated with lower case g's.

Upon crossing the first offspring, the filial or F one generation appear identical expressing the same phenotype of green pods. This result illustrates the Principle of Uniformity and indicates that green is the dominant trait of the two colors.

Now when plants of the F one generation are allowed to self-fertilize, their progeny, F two plants, contain some with green pods and others with yellow ones in a ratio of three to one. Which confirms that yellow is indeed the recessive trait, a hidden form carried down from the initial parents.