When you look at the answers you have from making the crosses:
.. the genotypic ratio is the ratio of “letter combinations” in the Punnett square. For instance, if a monohybrid cross produces RR, Rr, rR, rr, then the genotypic ratio is 1 RR: 2 Rr: 1 rr.
.. the phenotypic ratio is the ratio of traits expected among the offspring. For instance, if R = red and r=white, then the RR, Rr, rR, rr outcome from the previous example would yield 3 reds and 1 white. The phenotypic ratio is 3 red: 1 white.
Dihybrid crosses are done the same way. It’s just that dihybrid crosses have a 4×4 Punnett square and the ratio will be more complicated, like 9 green, round: 3 green, wrinkled: 3 yellow, round: 1 yellow, wrinkled.
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