Micah has straight hair. If he is homozygous for the gene that determines straight hair, what is true of his parents?

They have contributed same allele for straight hair.

Explanation:

There are two conditions homozygous and heterozygous. In homozygous conditions both the allele of a particular gene is same in an offspring which means the offspring got two same alleles from its parent for a particular gene and if an offspring is heterozygous for a gene that suggests that the parent has contributed two different alleles for that gene in the offspring.

So If Micah is homozygous for straight hair then it can be concluded that his parents have contributed two same alleles for straight hair genes.