A monohybrid cross between tall and dwarf pea plants. A heritable characteristic, such as the height of the plant, is called a phenotype.

The symbols D and d designate the tall and dwarf unit factors (genes), respectively, in the genotypes of mature plants (sporophytes) and gametes.

Sporophytes are shown in rectangles, and gametes are shown in circles.

In the F1 generation, all of the plants show just one of the two contrasting traits.