dominant over the other and when the resultant phenotype is a combination of the expression of both alleles. Thus, in F2 generations, where the original P generation crossed a homozygous dominant parent with a homozygous recessive one, both the genotypic and phenotypic ratios would be 1:2:1 since the heterozygous individuals do not express the dominant phenotype.
When a cross involves two characters, it is called a dihybrid cross. When a parent homozygous dominant for both characters is bred with a parent homozygous recessive for both characters, and when the genes for the two characters are independent genes, that is, are on located on non-homologous chromosomes, four different phenotypes result in the F2 generation having a ratio of 9:3:3:1. For example, a cross between an pea plant with green/inflated pods (both homozygous dominant characters) and a plant with yellow/constricted pods (both homozygous recessive characters) produces an F1 generation where the individuals all are heterozygous for both characters. In the F2 generation, nine individuals show both of the dominant expressions and bear green/inflated pods, three show the dominant expression of one character and the recessive expression of the other character and bear green/constricted pods, three show the opposite combination of a dominant expression of one character and the recessive expression of the other character and bear yellow/inflated pods, and one shows both of the recessive expressions and bears yellow/constricted pods. Although plants are created, such as the middle two
