Austrian monk and scientist Gregor Mendel unearthed the basic principles of inheritance by breeding pea plants. Peas are ideal for such experiments because they have such a wide variety of traits. He conducted numerous mate crossings with these plants, a number of them being monohybrid in that they combined parents differing in only a single trait, such as color or size. His findings serve as the blueprint for modern genetics.
Furthermore, a monohybrid, according to the Mendelian Genetics article on the North Dakota State University website, is "the offspring of two parents that are homozygous for alternate alleles of a gene pair." A gene pair refers to duplicate copies of a certain gene existing in a diploid cell. Alleles are alternatives to given forms of genes, or one of two somewhat differing forms of a gene that code for differing semblances of the same trait. Monohybrid inheritance describes the passing on of a single trait or characteristic over a generation.
Mendel's First Law -- otherwise known as the Law of Segregation -- affirms that alleles separate during the forming of gametes. This law is the basis for the conception of monohybrid crosses. Mendel concluded that each gamete carries just one part of the gene pair. Therefore, a single shared trait will influence inheritance, but the phenotype of hybrids can differ.
In practical genetics, the concept of monohybrid crosses is used to determine the phenotype traits of a third generation based on a duo of homozygous grandparents. For breeders of plants or animals, such information can be used to gauge and plan the characteristics of offspring.