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

Phenotype Round, yellow Wrinkled, green

Genotype RRYY rryy

Gametes all RY all ry

F1 all RrYy

All in F1 generation are heterozygous for both characteristics (all round and yellow)

X

P generation cross…

Phenotype Round, yellow

Genotype RrYy

Gametes RY, Ry, rY, ry

F2 We really need a punnet square for this…

X Round, yellow

RrYy

RY, Ry, rY, ry

F1 generation cross…

RY Ry rY ry

RY RRYY RRYy RrYY RrYy

Ry RRYy RRyy RrYy Rryy

rY RrYY RrYy rrYY rrYy

ry RrYy Rryy rrYy rryy

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...?