Name _______________________________ Class _____ Date ________________
Dihybrid Cross Worksheet
Review of a Monohybrid Cross which only compares ______ trait at a time:
B = brown hair and b = blonde hair.
Example:
Bb X Bb
Gametes:
B and b; B and b
Parents that are heterozygous for Brown hair
Each parent produces 2 gametes.
1. What are the chances of the offspring being homozygous brown haired?
2. What are the chances of the offspring having blonde hair?
3. What are the chances of the offspring being heterozygous brown haired?
4. What is the genotypic ratio?
_____: _____: _____
BB
Bb
bb
5. What is the phenotypic ratio? _______: ______
Brown Blonde
6. What is the dominant gene?
7. Is there a heterozygous blonde haired offspring?
Why?
A Dihybrid Cross compares ______ traits at a time:
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 that is heterozygous round seed shape and heterozygous yellow seed
color is crossed with a pea plant which is homozygous round seed and has green seed color.
Parents:
RrYy
Gametes:
(alleles)
RY
Ry
rY
ry
X
RRyy
In a dihybrid cross, you have to list ALL possible combinations
a parent can pass along because you don’t know which alleles
will be passed on to the next generation (Mendel’s Law of
Independent Assortment states that genes for different
traits are inherited independently of each other)
Ry
Ry
Ry
Ry
RY
Ry
rY
ry
Ry
Ry
Ry
Ry
1. What are the possible genotypes and phenotypes of the offspring?
2. What are the chances of the offspring for having a round shape? ____ out of ____
3. What are the chances of the offspring for having a wrinkled shape? ____ out of ____
4. What are the chances of the offspring for having yellow seeds? ____ out of ____
5. What are the chances of the offspring for having green seeds? ____ out of ____
6. What is the phenotypic ratio?
________: ________
Round & yellow Round & green
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:
Gametes:
(alleles)
__ __ __ __
_____
_____
_____
_____
Y = yellow seed color
y = green seed color
X
__ __ __ __
_____
_____
_____
_____
7. What are the possible genotypes and phenotypes of the offspring? There are 9 genotypes!
8. What are the chances of the offspring being homozygous for both round seed shape and yellow seed
color? ______ out of ______
9. What are the chances of the offspring being homozygous for both wrinkled seed shape and green
seed color? ______ out of ______
10.
What are the chances of the offspring being heterozygous for both shape and seed color? __/__
11. What are the chances of the offspring for having a round shape? ____ out of ____
12. What are the chances of the offspring for having a wrinkled shape? ____ out of ____
13. What are the chances of the offspring for having yellow seeds? ____ out of ____
14. What are the chances of the offspring for having green seeds? ____ out of ____
15. What is the phenotypic ratio? ________ : _______
: _______
: _______
Round & yellow Round & green Wrinkled & yellow Wrinkled & green
A purebred wingless red-eyed fruit fly is crossed with a purebred winged brown-eyed fruit fly to produce
F1 flies.
A = wings
a = wingless
E = red-eyes
e = brown-eyes
Parents:
__ __ __ __ X __ __ __ __
Gametes:
_____
_____
_____
_____
_____
_____
_____
_____
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: __ __ __ __ X __ __ __ __
Gametes:
_____
_____
_____
_____
_____
_____
_____
_____
16. What are the possible genotypes and phenotypes of the offspring?
17. Phenotypic ratio: ______________:______________:_______________:______________
Phenotypes 
SpongeBobs’ aunt, who is a roundpants, has a cute stubby nose. She has finally found the sponge of her dreams and is ready
to settle down. Her fiancé always comments on how adorable her stubby nose is (aww, how sweet!). They often wonder
what the chances are of that trait being passed on. Her fiancé is a purebred Squarepants and has a purebred long nose.
4. Identify the genotypes of the aunt and her fiancé using the alleles from the table above.
Aunt - Roundpants, Stubby Nose _________
Fiancé – Purebred Squarepants, Long Nose __________
5. What are the possible gamete combinations for each person? Aunt __________ Fiancé __________
6. Create a Punnett square to show the possible genotypes for their children.