Hybridization refers to the process of mating two individuals from different breeds which are genetically distinct.

Mating of two purebred parents that express different traits for only one characteristic is called a monohybrid cross. The example below shows a cross between two pea plants with yellow and green seeds respectively:

An example of hybridization using yellow and green peas. In the original, or P, generation, two peas are crossed, one yellow and one green. The yellow pea has the genotype capital y capital y, while the green pea has the genotype lowercase y lowercase y. Each pea passed on one gene to the next generation, a capital y from the yellow pea and a lowercase y from the green pea. The resulting offspring, called the F1 generation, is a pea with yellow phenotype and the genotype capital y lowercase y. In the F2 generation, two peas from the F1 generation are crossed. The inheritance is shown with a punnet square. The punnet square is used to show all possible gene combinations and resulting phenotypes in the F2 offspring. The punnet square is a table containing two rows and two columns. Both F1 peas have the genotype capital y lowercase y, so the first column in the punnet square is labelled with a capital y and the second column with a lowercase y. The first row is labeled with a capital y and the second row is labelled with a lowercase y. The F2 genotypes and phenotypes from the punnet square are as follows. Column 1, row 1: yellow pea with capital y capital y genotype. Column 2, row 1: yellow pea with capital y lowercase y genotype. Calum 1, row 2: yellow pea with capital y, lowercase y genotype. Column 2, row 2: green pea with lowercase y, lowercase y phenotype.

Figure 1: Monohybrid cross.

All seeds of the first (F1) generation have yellow phenotypes, because the yellow seed color is dominant over the green seed color. In the second generation (F2) the ratio between yellow and green seeds becomes 3:1 three to one as depicted in the Punnet square.