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GgTt x GgTt F2=
A dihybrid cross is a cross between a P generation that differs in two traits rather than one. For example, a pea plant that is homozygous for the dominant green pod color (GG), and dominant tall height (TT) crossed with a pea plant that is homozygous for the recessive yellow pod color (gg) and recessive short height (tt) will produce hybrid offspring that are heterozygous for pod color and height (GgTt), and will have green pod color and tall height. GGTT x ggtt --> GgTt
The cross RR X Dd is showing two different genes for the parents (it is showing RR for one parent and Dd for the other) - therefore this is not a dihybrid cross. However, if it was RRDd X RRDd, this would be a dihybrid cross. For a dihybrid cross, you need to include two different genes (and show these genes in both the parents). So - BbFf X bbff, GGTT X ggtt, KKPp X KkPp - are all examples of dihybrid crosses.