Rachel and Steve both have tightly curled hair. (The hair form gene shows incomplete dominance. There are two alleles, curly and strait. The heterozygote has wavy hair). Rachel has a child with wavy hair. Is it possible for Steve to be the father of this child? Why or why not?

Hair form gene shows incomplete dominance. So if C is responsible for curly hair and c is responsible for straight hair,

CC = Curly

Cc = Wavy

cc = straight

Rachel has curly hair so her genotype is CC. She has a child with wavy hair. Wavy hair is produced by Cc. Since the child got C allele from Rachel, he must have got c allele from the father. So, the father should have at least one c allele. Steve has curly hair so his genotype is CC. Since Steve does not have even one c allele, he can not be the father of Rachel's child.