Mendelian Genetics

Question

A man who is a PTC taster with a continuous hairline marries a PTC taster with a widow's weak. They have two children, one with a widow's peak who is a non-taster and the other who has a continuous hairline and is a PTC taster. The man remarries and has 9 children who are all PTC tasters with a widow's peaks. His second wife has the same phenotype as their 9 children. What are the genotypes of this man and his two wives? (PTC taster dominant to non taster and widow's peak dominant to continuous)

Answer 1

First, assign letters to each trait.  P = PTC Taster; p = non-taster;  W=widow's peak; w=continuous

 

Second, write the genotypes for the man and woman.  Man =  P?ww  x   P?W?   1st wife

We don't yet know if the genotypes are heterozygous or homozygous for certain traits.

 

Third, look at children.  One:  ppW?; Second:  P?ww 

What does this tell us?  Child #2 has two w alleles so one had to come from each parent.  Child #1 has two p alleles so one had to come from each parent. Fill in the two ?  

So the parent genotypes are now known to be  Man  Ppww;  1st wife  PpWw

 

Now on to the 2nd wife:  9 children:  P?W?      Dad:  Ppww

What is 1st wife's genotype?   Must be P?Ww   Could be PPWw  or PpWw