In humans having a wide jaw (W) is completely dominant to having a narrow jaw (w). Having large teeth (L) is completely dominant to having small teeth (t). A man with a wide jaw whose mother has a narrow jaw is heterozygous for teeth size. He marries a woman who has a narrow jaw and is heterozygous for large teeth. What are the two parents genotypes?

Answer: The man's genotype is WwLt while the woman's genotype is wwLt.

Explanation: From the information given above, W is the allele for wide jaw, w is the allele for narrow jaw, W is completely dominant to w, L is the allele for large teeth while t is the allele for small teeth.

The man has wide jaw but his mother has a narrow jaw, since narrow jaw is recessive the man must have inherited one recessive allele for narrow jaw from his mother who has two recessive alleles for narrow jaw. Therefore since the man has wide jaw, he must be heterozygous for wide jaw (having one dominant allele for wide jaw and one recessive allele for narrow jaw), his genotype for wide jaw is therefore Ww. The man is heterozygous for teeth size, this means that he has one dominant allele for large teeth and one recessive allele for small teeth. His genotype for teeth size is Lt. Therefore the man's genotype is WwLt.

The woman has a narrow jaw, this means that she has two recessive alleles for narrow jaw (ww) and she is heterozygous for large teeth size, this means that she has one dominant allele for large teeth and one recessive allele for small teeth (Lt). Therefore, the woman's genotype is wwLt.