A woman with curly hair and a man with straight hair produced kids with straight hair:

Question

1. complete dominant 
2. incomplete dominant
3. codominant 

Answer 1

We would assume in this scenario that the dominant trait is straight hair, since the offspring are 100% straight hair.

We will assign alleles to each trait.

A = Straight Hair

a = Curly Hair

Since the mother has curly hair, her genotype must be (aa). The father could be (AA) or (Aa), but since we know the children are 100% straight hair, the father would be (AA)

In a cross between (aa) x (AA), the result would be 100% heterozygous, straight-haired, children.

Based on the limited information from this question, this would be a complete dominance question.

Answer 2

Complete dominance of an allele occurs when the dominant trait completely masks the recessive trait. In this case, the dominant trait is straight hair and the recessive trait is curly hair.

Incomplete dominance is when there is a blend of the dominant and recessive traits.

Codominance occurs when both the dominant and recessive traits are present, without a blend.

A commonly used example is a flower:

Imagine a red flower and a white flower, where the color red is the dominant trait (RR) and the color white is the recessive trait (rr). Incomplete dominance in the offspring flowers would show up as a mixture of red and white (Rr), showing up as a pink flower. Codominance would also present as Rr, but the offspring flowers would be a mixture of red and white portions.