SBI 3C
Incomplete and Co-dominance Worksheet
1) Explain the difference between incomplete and co-dominance.
Co-dominance Problems
2) In some chickens, the gene for feather colour is controlled by codominance. The allele for black is B and the
allele for white is W. The heterozygous phenotype is known as erminette (black and white spotted)
a. What is the genotype for black chickens? ________________
b. What is the genotype for white chickens? ________________
c. What is the genotype for erminette chickens? ________________
3) If two erminette chickens were crossed, using a Punnett Square determine the probability that:
a. They would have a black chick?
b. They would have a white chick?
Parents: ______x ________
4) A black chicken and a white chickem are crossed. What is the probability that they will have erminette chicks?
Show using a Punnett Square.
Parents: ______x ________
SBI 3C
In shorthorn cattle, when a roan bull (RR) is crossed with a white cow (WW), all the offspring are roan – a spotted, red
and white or milky red colour.
5) What offspring are expected from a cross between a red bull and a roan cow? Show using a Punnett Square.
Parents: ______x ________
6) What phenotypes would you expect from a cross between a red bull and white cow? Show using a Punnett
Square.
Parents: ______x ________
7) Two short-tailed cats are bred together. They produce three kittens with long tails, five with short tails, and two
without any tails at all. From these results, how do you think tail length is these cats is inherited? Show all of the
genotypes for the parents and the offspring to support your answer.
SBI 3C
Incomplete Dominance Problems
8) In snapdragons, flower colour is controlled by incomplete dominance. The two alleles are red (R) and white (R’).
The heterozygous genotype is expressed as pink.
a. What is the phenotype of a plant with genotype RR? ____________
b. What is the phenotype of a plant with genotype R’R’? ____________
c. What is the phenotype of a plant with genotype RR’? ____________
9) A pink-flowered plant is crossed with a white flowerd plant. What is the probability of producing a pink-flowered
plant? Show using a Punnett Square.
Parents: ______x ________
10) What plants would you need to cross to produce the most pink-flowered plants? Show using a Punnett Square.
Parents: ______x ________
11) In Andalusian fowls, feather black feathers (B) are incompletely dominant over white individuals (B’). A
homozygous black bird is crossed with a homozygous white bird. The offspring are all bluish-grey. Show the
cross as well as the genotypes and phenotypes of the parents and offspring.
12) If two bluish-grey individuals were crossed, what would be the ratios for both phenotype and genotype of the
offspring.