Name: ______________________
Date: _______________ Per: ____
Incomplete/ Codominance Bonanza
Directions: Answer the following genetic cross problems. It is essential that you know the all of the
vocabulary included in this worksheet as well. Remember when you are doing a genetic cross to follow
the steps below to complete! MUST SHOW ALL WORK!
STEP 1: Determine what kind of problem you are trying to solve.
STEP 2: Determine letters you will use to specify traits.
STEP 3: 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.
1. In guinea pigs, the allele for short hair is dominant.
a. What genotype would a heterozygous short haired guinea pig have?
b. What genotype would a purebreeding short haired guinea pig have?
c. What genotype would a long haired guinea pig have?
2. Two short haired guinea pigs are mated several times. Out of 100 offspring, 25 of
them have long hair. What are the probable genotypes of the parents?
__________ x ___________ Show the cross to prove it!
3. In the 1950’s, a young woman sued film star/director Charlie Chaplin for parental
support of her illegitimate child. Charlie Chaplin’s blood type was already on
record as type AB. The mother of the child had type A and her son had type O
blood.
a. Complete a Punnett square for the possible cross of Charlie and the mother.
b. The judge ruled in favor of the mother and ordered Charlie Chaplin to pay child
support costs of the child. Was the judge correct in his decision based on blood
typing evidence? Explain why or why not. *refer to any Punnett squares to
support your answer.
Name: ______________________
Date: _______________ Per: ____
4. In snapdragons, red is not completely dominant over white flowers. What color
flowers would you expect when you cross a red flower with a white flower? What
would be the genotypic and phenotypic ratios of the offspring be?
5. What would you expect from a cross between two pink flowers from above? Give
genotypic and phenotypic ratios.
Roan Cow
6. In cattle red hair color and white hair color are co-dominant. A cross between a
white and a red cow produces a roan colored cow. Cross a red-haired and roan
colored cow. What are the genotypic and phenotypic ratios of offspring?
7. In a pea plants the tall allele (T) show complete dominance over the short (t).
You can tell if a tall plant is homozygous or heterozygous by performing a test
cross. Explain a test cross and show the punnett square test crosses for both
the homozygous and heterozygous pea plant.