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NOTES - Simple Dominance, Incomplete Dominance, and Codominance
Some genes have alleles that are dominant and recessive, but some do not.
Genes with alleles that are not dominant or recessive create more than two
phenotypes.
Simple Dominance 
Ex.
Incomplete Dominance –


Ex.
Codominance –


Ex.
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Problems
1. In a certain type of flower, the flower color gene has two alleles - red
flowers (r) and yellow flowers (y). Heterozygous flowers (ry) are orange.
a. Is this an example of simple dominance, incomplete dominance, or
codominance? How do you know?
b. Cross two orange-flowered plants. Give the genotypic and
phenotypic % of the offspring.
c. If the cross above produced 100 offspring, how many would you
expect of each phenotype? How many of each genotype?
2. In snapdragons, the red flower color (r) and white flower color (w) are
incompletely dominant alleles. Heterozygous organisms (rw) are pink.
a. Cross a red flower with a white flower. Give the genotypic and
phenotypic % of the offspring.
b. Cross one of the offspring from question a with a red flower. Give
the genotypic and phenotypic % of the offspring.
c. Cross one of the offspring from question a with a white flower. Give
the genotypic and phenotypic % of the offspring.
3. In certain breeds of horses, the coat color gene has two alleles – brown
coat (B) and white coat (W). Heterozygous horses (BW) have both colors
in their coat, this is called roan.
a. Is this an example of simple dominance, incomplete dominance, or
codominance? How do you know?
b. Cross a brown horse with a white horse. Give the genotypic and
phenotypic % of the offspring.
c. Cross two roan horses. Give the genotypic and phenotypic % of
the offspring.
4. In Erminette chickens, black feathers (B) and white feathers (W) are
codominant alleles. Heterozygous chickens have some all black feathers
and some all white feathers.
a. Cross a heterozygous chicken with a black feathered chicken. Give
the genotypic and phenotypic % of the offspring.
b. Cross two heterozygous chickens. Give the genotypic and
phenotypic % of the offspring.
5. In pea plants, round seeds (R) are dominant over wrinkled seeds (r).
a. Is this an example of simple dominance, incomplete dominance, or
codominance? How do you know?
b. Cross a homozygous recessive plant with a heterozygous plant.
Give the genotypic and phenotypic % of the offspring.
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