Dihybrid cross = involves inheritance of 2 characteristics

Example 1:

In Pisum sativum, a round seed is produced by a dominant allele (R), while wrinkled seeds are produced by the recessive allele (r).  Yellow seeds are produced by the dominant allele (Y), while green seeds are produced by the recessive allele (y).

In a cross between a homozygous round, yellow plant and a wrinkled green plant, what is the F1 and F2 phenotypic and genotypic ratio?

Key:       R = round seed                  Y = yellow seeds

r = wrinkled seed                y = green seeds

P1:     round yellow seed            x wrinkled green seed

RRYY                                                     rryy

Gametes:  R, Y                                                r, y

ryry
RYRrYyRrYy
RYRrYyRrYy

F1: Genotypic Ratio: 100% heterozygous RrYy

Phenotypic Ratio: 100% round, yellow seeds

F2:   Crossing F1 plants among themselves produces an F2 generation.

P2: round yellow seed x round yellow seeds:

RrYy                        RrYy

Possible Gametes:

RY, Ry, rY, ry              RY, Ry, rY, ry

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