Co-Dominance
In chickens, feather color exhibits co-dominance. If you cross a chicken with black feathers with a rooster with
white feathers, the offspring will have speckled black and white feathers. Both traits are being expressed
together. Black and white are both present in the offspring.
KEY
Genotype
Phenotype
1. Cross a black chicken with a white rooster.
P1:
P2:
Genotypes:
Phenotypes:
2. What are the possible offspring of a cross between a black chicken and a speckled rooster?
P1:
P2:
Genotypes:
Phenotypes:
3. Clucky is black and his sister is speckled. If his parents are both speckled, how is this possible?
Genotypes:
P1:
P2:
Phenotypes:
4. What was the probability that Clucky would be black and his sister would be speckled?
KEY
Genotype
Phenotype
Red cows have a dominant red allele and white cows have a dominant white allele. When a red cow mates with
a white bull, they can have offspring that have the color that is called Roan which is a red and white spotted
appearance. This is an example of co-dominance.
5. What are the possible offspring if you mate a roan cow with a red bull?
P1:
Genotypes:
Phenotypes:
P2:
6. Mate a roan cow with a roan bull.
P1:
Genotypes:
P2:
Phenotypes:
7. Moo is a white cow. What percentage of Moo's offspring will be white if she finds a nice Roan bull to
mate with?
P1:
Genotype:
P2:
Phenotype:
8. Moo is a white cow. Her brother is a roan bull. None of the siblings are red. What are the possible
genotypes of the parents?
Offspring 1:
Offspring 2:
No Offspring:
Genotype P1:
Genotype P2:
Incomplete Dominance
1. Coat color in mice is incompletely dominant. Yellow and white-colored mice are
homozygous, while cream-colored mice are heterozygous. If two cream-colored mice mate,
what phenotypic ratio can we expect of their offspring? Show the Punnett Square.
P1:
Genotypes:
P2:
Phenotypes:
2. In radishes, red and white are pure-breeding colors, while hybrids are purple. If a red radish is
crossed with a white radish, what will be the phenotype of the F2 generation (assuming the F1
generation self-pollinates)? Show the Punnett Square.
P1:
Genotypes:
P2:
Phenotypes:
3. In snapdragons, flower color is controlled by incomplete dominance. The two alleles are red
(R) and white (W). The heterozygous genotype is expressed as pink.
a) What is the phenotype of a plant with the genotype RR? ___________
b) What is the phenotype of a plant with the genotype WW? ___________
c) What is the phenotype of a plant with the genotype RW? ___________
4. A pink-flowered plant is crossed with a white-flowered plant. Show the Punnett Square. What is
the probability of producing a pink-flowered plant? ____%
P1:
Genotypes:
P2:
Phenotypes:
5. What cross will produce the most pink-flowered plants? Show a punnett square to support your
answer.
P1:
Genotypes:
P2:
Phenotypes:
6. In Andalusian fowls, black individuals (B) and white individuals (W) are homozygous. A
homozygous black bird is crossed with a homozygous white bird. The offspring are all bluishgray. Show the cross as well as the genotypes and phenotypes of the parents and offspring.
P1:
Genotypes:
P2:
Phenotypes:
7. What are the genotypic and phenotypic ratios if a black individual is crossed with a bluishgray individual? Show the Punnett Square.
P1:
Genotypes:
P2:
Phenotypes:
8. If two bluish-gray individuals were crossed, what would be the ratios for both phenotype and
genotype of the offspring? Show the Punnett Square.
P1:
Genotypes:
P2:
Phenotypes:
Multiple Alleles/Blood Types
Fill in the table below to use as your key for the blood typing problems. For each of the problems below, use
your blood type key. Show work for ALL problems!!! Don’t forget to answer the question that is being asked.
Phenotype
Genotype (s)
Type A
Type B
Type AB
Type O
1. Suppose a woman with blood type O married a man with blood type AB. What phenotypes and genotypes
would you expect to observe in their offspring, and in what ratios?
P1:
Genotypes:
P2:
Phenotypes:
2. What is the expected genotypic ratio among children born to a mother having the genotype AO and a father
with the phenotype AB?
P1:
Genotypes:
P2:
Phenotypes:
3. One parent has the blood type A and the other blood type B. What are the genotypes of the parents if they
produce children with only blood type AB?
P1:
Genotypes:
P2:
Phenotypes:
4. One parent has the blood type A and the other blood type B. What are the genotypes of the parents if 1/2 the
offspring are AB and the other 1/2 A?
P1:
Genotypes:
P2:
Phenotypes:
5. One parent has the blood type A and the other blood type B. What are the genotypes of the parents if the
offspring produce the following blood types...1/4 AB, 1/4 A, 1/4 B, and 1/4 O?
P1:
Genotypes:
P2:
Phenotypes:
6. An actress claimed that the movie star, Charlie Chaplin, was the father of her child. Her blood type was type
A, the child’s was type B and Chaplin’s was type O. The first jury could not agree on a verdict and the second
jury found him guilty. Comment on the verdicts (show your work to prove it!). (A historical note: at the time
of these trials, blood typing did not meet the court standards for scientific evidence.)
P1:
Genotypes:
P2:
Phenotypes:
SEX Linked
In fruit flies, eye color is a sex linked trait. Red (R) is dominant to white (r).
1. What are the sexes and eye colors of flies with the following genotypes:
XRXr
_________________
XRY
_________________
XRXR
_________________
XrY
_________________
2. What are the genotypes of these flies:
white eyed, male ____________
red eyed female (heterozygous) ________
white eyed, female ___________
red eyed, male ___________
3. Show the cross of a white eyed female X r
X r with a red-eyed male X R Y
.
4. Show a cross between a pure red eyed female and a white eyed male.
What are the genotypes of the parents:
___________& _______________
How many are:
white eyed, male___
white eyed, female ___
red eyed, male ____
red eyed, female ____
5. Show the cross of a red eyed female (heterozygous) and a red eyed male. What are the genotypes of the
parents?
___________ & ___________
How many are:
white eyed, male___
white eyed, female ___
red eyed, male ____
red eyed, female ____
Math: What if in the above cross,
100 males were produced and 200
females.
How many total red-eyed flies
would
there be?
6. In humans, hemophilia is a sex linked trait. Females can
be normal,
carriers, or have the disease. Males
will either have the disease or not (but they won’t ever be carriers)
____________
= female, normal
= male, normal
= female, carrier
= male, hemophiliac
= female, hemophiliac
7. Show the cross of a man who has hemophilia with a woman who is a carrier.
P1:
Genotypes:
P2:
Phenotypes
What is the probability that their children will have the disease? __________
8. A woman who is a carrier marries a normal man. Show the cross. What is the probability that
their children will have hemophilia? What sex will a child in the family with hemophilia be?
P1:
Genotypes:
P2:
Phenotypes
9. A woman who has hemophilia marries a normal man. How many of their children will have hemophilia, and
what is their sex?
P1:
Genotypes:
P2:
Phenotypes
10. In cats, the gene for calico (multicolored) cats is co-dominant. Females that receive a B and an R gene
have black and orange splotches on white coats. Males can only be black or orange, but never calico.
B
R
Here’s what a calico female’s genotype would look like.
X
X
Show the cross of a female calico cat with a black male?
P1:
Genotypes:
P2:
Phenotypes
What percentage of the kittens will be black and male? _________
What percentage of the kittens will be calico and male? _________
What percentage of the kittens will be calico and female? _________
11. Show the cross of a female black cat, with a male orange cat.
P1:
What percent of kittens will be calico and female?
What color will all the male cats be?
P2:
Types of basic genetics problems
Complete
Dominance
Incomplete
Dominance
Co-dominance
Blood Types
Characteristics:
Characteristics:
Characteristics:
Characteristics:
Example:
Example:
Example:
Example:
Sex-Linked
Example