Download Worksheet: Dihybrid Crosses

Worksheet: Two-Factor Crosses (Di-hybrid)
STEP 1: Determine what kind of problem you are trying to solve.
STEP 2: Determine letters you will use to specify traits.
STEP 3: Use the FOIL method to determine parent’s genotypes.
STEP 4: Make your Punnett square and make gametes
STEP 5: Complete cross and determine possible offspring.
STEP 6: Determine genotypic and phenotypic ratios.
TTGG ttgg
**Use the KEY in the example below for questions 1-4**
Example: A tall green pea plant (TTGG) is crossed with a short white pea plant (ttgg).
KEY: TT or Tt = tall
green gg = white
Cross: TTGG
X
tt = short
GG or Gg =
tg
tg
tg
tg
TG
TtGg
TtGg
TtGg
TtGg
ttgg
F: TG
F: tg
O: TG
O: tg
TG
TtGg
TtGg
TtGg
TtGg
I: TG
I: tg
TG
TtGg
TtGg
TtGg
TtGg
L: TG
L: tg
TG
TtGg
TtGg
TtGg
TtGg
Genotypic Ratio:
16 TtGg
Phenotypic Ratio: 16 Tall/Green
1) Cross a tall, heterozygous green pea plant (TTGg) with a heterozygous tall ,green pea plant (TtGg).
Key: T = tall
t = short
G = green
g = white
Cross: ___________ X ___________
F: _________ F: _________
O: _________ O: _________
I: _________
I: _________
L: _________
L: _________
Genotypic Ratio:
Phenotypic Ratio:
2) A tall green pea plant (TtGg) is crossed with a Short white pea plant (ttgg).
Key: T = tall
t = short
G = green
g = white
Cross: ___________ X ___________
F: _________
F: _________
O: _________
O: _________
I: _________
I: _________
L: _________
L: _________
Genotypic Ratio:
Phenotypic Ratio:
3. Sleeping Beauty is known throughout the kingdom for her beautiful homozygous ruby red lips and golden hair.
The prince that has awakened her from her slumber has heterozygous red lips and heterozygous black hair. Red
lips are dominant and pink lips are recessive. Black hair is dominant and blonde hair is recessive.
a. Construct a dihybrid cross to determine what their children might look like.
b. What are the expected genotype and phenotype ratios of their offspring?
Cross: ___________ X ___________
F: _________ F: _________
O: _________ O: _________
I: _________
I: _________
L: _________
L: _________
Genotypic ratio:
Phenotypic ratio:
4. Cinderella is so happy! She is marrying her Prince Charming and preparations are underway for the wedding
ceremony. She wants everything to be perfect, right down to the flowers. Her favorite colors are pink and red,
but alas – only pink roses are available. Not only is Cinderella an excellent housekeeper, she also has a
background in Biology, so she directs the palace gardeners to cross pink roses with pink roses. She knows that
roses show incomplete dominance and that pink roses have a heterozygous genotype, while one homozygous
genotype shows red roses and the other homozygous genotype shows white roses.
a. Construct a Punnett square for the cross of pink roses X pink roses.
b. What is the expected phenotype ratio? Will Cinderella have pink and red roses for her wedding?
Genotypic ratio:
Phenotypic ratio:
5. Wolves are sometimes observed to have black coats and blue eyes. Assume that these traits are controlled
by single genes that are located on two different chromosomes. Assume further that normal coat color is
dominant to black coat color and that brown eyes are dominant to blue eyes. Suppose a male wolf with a
black coat and blue eyes mates with a female wolf heterozygous for both normal coat color and brown eyes.
a. Construct a Punnett square to see what the resulting pack might look like.
b. What is the expected phenotype and genotype ratio?
Genotypic ratio:
Phenotypic ratio:
6. In monsters, eye color is a trait that exhibits co-dominance. Monsters that are RR have red eyes, those that are
YY have yellow eyes, and monsters that are heterozygous have red AND yellow freckled eyes.
a. If a yellow-eyed monster marries a monster with red AND yellow freckled eyes, what are the
expected genotype and phenotype ratios of their mini-monsters (children)?
b. Mortimer and Matilda Monster have three children, Mavis has red AND yellow freckled eyes, Mabel
has red eyes, and Mort Jr. has yellow eyes. Use the phenotypes of the children to determine the
genotypes of the parents, Mortimer and Matilda.
7. In Kingwood Texas, there is a creature known as a panther. It comes in three colors, yellow, green, and
blue. This trait is controlled by a single gene with incomplete dominance. A homozygous (YY) individual is
yellow, a homozygous (Y’Y’) individual is blue, and a heterozygous (YY’) individual is forest green.
a. What would be the genotypic and phenotypic ratios of the offspring if a yellow panther were
crossed with a blue one?
Genotypic ratio:
Phenotypic ratio:
Matching -Match the term with the correct definition
________1. Combination of alleles that contains a dominant and recessive
________2. Study of heredity
________3. Haploid reproductive cells
________4. Humans have 23 pair of these
________5. Unit on a chromosome that codes for a trait
________6. Type of allele that is always expressed when present
________7. Separation of alleles when homologous pairs separate
________8. Having two of the same alleles
________9. Traits passed on from parents to offspring
________10. Outward appearance of an organism
________11. Characteristic that distinguishes one individual from another
________12. Different forms of a gene
________13. Type of allele that is masked when there is only one present
________14. Genetic composition of an organism
________15. Cell that contains pairs of chromosomes, 2n
________16. Fertilized egg
A.
B.
C.
D.
E.
F.
G.
H.
I.
J.
K.
L.
M.
N.
O.
P.
Q.
Allele
Chromosomes
Diploid
Dominant
Gamete
Gene
Genetics
Genotype
Haploid
Heredity
Heterozygous
Homozygous
Law of segregation
Phenotype
Recessive
Trait
Zygote