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Codominance Worksheet
(ALWAYS make a KEY!)
Period_____
Name_____________________
1. The palomino horse is a hybrid exhibiting a golden color with a lighter mane and
tail. A pair of alleles (D1 & D2) is known to be involved in the inheritance of these coat
colors. Genotypes homozygous for the D1 allele are Chestnut colored (reddish);
heterozygous genotypes are Palomino colored; and genotypes that are
homozygous for the D2 allele are Cremello (almost white). KEY: D1D1 D2D2 D1D2 (a.) Two palominos were crossed. Predict the following:
Parents’ phenotypes:
Punnett square:
Parents’ genotypes:
Offspring genotypes (with prob.):
Offspring phenotype (with prob.):
(b.) What kind of mating will produce ONLY palominos?
(c.) What kind of inheritance is this - codominance or incomplete dominance?
2. Yellow coat color in guinea pigs is produced by the homozygous genotype
CYCY, cream color by the heterozygous genotype CYCW, and white by the
homozygous genotype CWCW. (What kind of inheritance?)
KEY:
(a) A yellow and a white guinea pig were crossed. Predict the following:
P1 phenotype:
Punnett square:
P1 genotypes:
F1 genotype (with prob.):
F1 phenotype (with prob.):
(b) The F1 were allowed to breed. Predict the following:
F2 genotype (with prob.):
F2 phenotype (with prob.):
Punnett square:
Sickle Cell Anemia (Kind of inheritance: incomplete dominance or codominance?)
In Sickle Cell Anemia, virtually all of the red blood cells in the homozygous BS
individual, will shrivel to a sickle shape when exposed to reduced oxygen tension.
This results in severe anemia and often a fairly early death of the individual.
Carriers (heterozygous individuals) have about half normal and half sickleshaped red blood cells, and may experience mild anemia. Carriers also have a
resistance to malaria. (Use BN for the normal allele.)
NOTE: Hemoglobin of “sicklers” differs in only one amino acid of the nine that
make up the specific peptide of normal hemoglobin. In this case, valine replaces the
normal glutamic acid.
KEY:
3. A person with normal red blood cells marries a person who is a carrier. Predict
the following:
Punnett square:
Parents’ phenotypes:
Parents’ genotypes:
Offspring genotypes (with prob.):
Offspring phenotype (with prob.):
4. Two carriers marry. Predict the following:
Parents’ phenotypes:
Punnett square:
Parents’ genotypes:
Offspring genotypes (with prob.):
Offspring phenotype (with prob.):
5. Radish shape may be long (SLSL), round (SRSR), or oval (SLSR).
(Kind of inheritance:______________________
If long radish is mated to an oval radish, predict the following:
Punnett square:
Parents’ phenotypes:
Parents’ genotypes:
Offspring genotypes (with prob.):
Offspring phenotype (with prob.):