Dihybrid Crosses

1
Dihybrid Crosses
2
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

3
P generation cross
X
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)
4
F1 generation cross
X
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
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RY Ry rY ry
RY RRYY RRYy RrYY RrYy
Ry RRYy RRyy RrYy Rryy
rY RrYY RrYy rrYY rrYy
ry RrYy Rryy rrYy rryy
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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
7
Now for trihybrid Crosses...?