A monohybrid cross is a type of genetics breeding experiment between two parent organisms that each have a different homozygous trait. An example is a cross between a pea plant with a dominant green seed and one with a recessive yellow seed. The offspring are all born with green seeds.
Monohybrid cross experiments were popularized by the Austrian monk Gregor Mendel, who did many such experiments with garden peas. Mendel crossed pea plants that differed in a single trait that was easy to observe, such as seed texture, seed color, flower color or growth habit. By observing the offspring of these crossbreeding experiments, Mendel was able to make predictions regarding which traits were dominant and which were recessive.