Dihybrid Crosses

Two characteristics at once… Dihybrid crosses are where we consider heredity in two characteristics at the same time. There are four possible combinations of two characteristics. Example: Pea color and shape. Peas can be... 1) round and yellow 2) round and green 3) wrinkled and yellow 4) wrinkled and green

X P generation cross… rryy RRYY Phenotype Round, yellow Wrinkled, green rryy RRYY Genotype all RY all ry Gametes all RrYy F1 All in F1 generation are heterozygous for both characteristics (all round and yellow)

X F1 generation cross… RrYy RrYy RY, Ry, rY, ry RY, Ry, rY, ry Phenotype Round, yellow Round, yellow RrYy RrYy Genotype RY, Ry, rY, ry RY, Ry, rY, ry Gametes F2 We really need a punnet square for this…

RY Ry rY ry RRYY RRYy RrYY RrYy RRyy Rryy rrYY rrYy rryy

This is the typical ratio expected in an F1 dihybrid cross F2 generation ratio : : : 9 3 3 1 Round Yellow Round Green Wrinkled Yellow Wrinkled Green This is the typical ratio expected in an F1 dihybrid cross

Now for trihybrid Crosses...?