Name _________KEY______________________ Class _____ Date ____________________
Dihybrid Cross Worksheet
In peas, round seed shape (R) is dominant to wrinkled seed shape (r), and yellow seed
color (Y) is dominant to green seed color (y). A pea plant which is homozygous round
seed and has green seed color is crossed with a pea plant that is heterozygous round seed
shape and heterozygous yellow seed color.
Example:
Gametes:
RRyy X
Ry
Ry
Ry
Ry
RrYy
RY
Ry
rY
ry
Punnet Square:
Gametes
Ry
RY
RRYy
Ry
RRyy
rY
RrYy
ry
Rryy
Ry
RRYy
RRyy
RrYy
Rryy
Ry
RRYy
RRyy
RrYy
Rryy
Ry
RRYy
RRyy
RrYy
Rryy
1. What are the chances of the offspring being homozygous for round seed? 8/16 = ½ = 50%
2. What are the chances of the offspring being homozygous for wrinkled seed? 0/16 = 0%
3. What are the chances of the offspring being homozygous for yellow seed color? 0/16 = 0%
4. What are the chances of the offspring being homozygous for green seed color? 8/16 = ½ = 50%
5. What are the chances of the offspring being heterozygous for both seed shape and
color? 4/16 = ¼ = 25%
Why? The chances of the offspring being heterozygous for both seed
shape and color is 25% because all gametes from one parent are Ry and 25% of the gametes from
the other parent are rY. So, there is a 25% of the offspring being heterozygous for both seed shape
and color.
6. What is the genotypic ratio? 25% RRYy; 25% RRyy; 25% RrYy; 25% Rryy
7. What is the phenotypic ratio? 50% round, yellow seeds; 50% round, green seeds
In the following plants round seed shape is dominant over wrinkled seed shape and
yellow seed color is dominant over green seed color. Determine the offspring
expected when two pea plants, each heterozygous for seed shape and seed color, are
crossed.
R = round seed shape
r = wrinkled seed shape
Parents:
R r Yy
Gametes:
RY
Ry
rY
ry
Y = yellow seed color
y = green seed color
X
R r Yy
RY
Ry
rY
ry
Punnett Square:
Gametes
RY
RY
RRYY
Ry
RRYy
rY
RrYY
ry
RrYy
Ry
RRYy
RRyy
RrYy
Rryy
rY
RrYy
RrYy
rrYY
rrYy
ry
RrYy
Rryy
rrYy
rryy
8. What are the chances of the offspring being homozygous for both round seed
shape and yellow seed color? 1/16 = 6.25% RRYY
9. What are the chances of the offspring being homozygous for both wrinkled seed
shape and green seed color? 1/16 = 6.25% rryy
10. What are the chances of the offspring being heterozygous for both shape and seed
color? 4/16 = 25% RrYy
11. What is the genotypic ratio? 1/6 RRYY; 2/16 RRYy; 2/16 RrYY; 1/16 RRyy; 4/16 RrYy;
1/16 rrYY; 2/16 Rryy; 2/16 rrYy; 1/16 rryy
12. What is the phenotypic ratio? 9:3:3:1
9/16 round, yellow seeds (DOM-DOM)
3/16 round, green seeds (DOM-REC)
3/16 wrinkled, yellow seeds (REC-DOM)
1/16 wrinkled, green seeds (REC-REC)
A purebred wingless red-eyed fruit fly is crossed with a purebred winged sepia-eyed fruit
fly to produce F1 flies.
A = wings
Parents: a a E E X
A A e e
a = wingless
E = red-eyes
e = sepia-eyes
Gametes:
aE
Ae
aE
Ae
aE
Ae
aE
Ae
Punnett Square:
Gametes
Ae
aE
AaEe
aE
AaEe
aE
AaEe
aE
AaEe
Ae
AaEe
AaEe
AaEe
AaEe
Ae
AaEe
AaEe
AaEe
AaEe
Ae
AaEe
AaEe
AaEe
AaEe
Two of the F1 flies are mated to produce an F2 generation of flies. What is the phenotypic
ratio of the F2 flies?
F2 Parents: A a E e
Gametes:
X
AE
Ae
aE
ae
A a E e
AE
Ae
aE
ae
Punnett Square:
Gametes
AE
AE
AAEE
Ae
AAEe
aE
AaEE
ae
AaEe
Ae
AAEe
AAee
AaEe
Aaee
aE
AaEE
AaEe
aaEE
aaEe
ae
AaEe
Aaee
aaEe
aaee
Genotypic ratio: 1/16 AAEE; 2/16 AAEe; 2/16 AaEE; 1/16 AAee; 4/16 AaEe; 1/16 aaEE;
2/16 Aaee; 2/16 aaEe; 1/16 aaee
Phenotypic ratio:
9/16 winged with red eyes (DOM-DOM)
3/16 wingless with red eyes (REC-DOM)
3/16 winged with sepia eyes (DOM-REC)
1/16 wingless with sepia eyes (REC-REC)