Elizabeth is married to John, and they have four children. Elizabeth has a straight nose (recessive) and is able to roll her tongue (dominant). John is also able to roll his tongue, but he has a convex (Roman) nose (dominant). Of their four children, Ellen is just like her father, and Dan is just like his mother. The other children—Anne, who has a convex nose, and Peter, who has a straight nose—are unable to roll their tongues. Please answer the following questions about this family.

Question

Diagram the three described generations of this family in accepted pedigree form, including the phenotypes for these two traits.

Answer 1

C: convex nose line; c: straight R: tongue roller; r: non roller
Elizabeth John
ccR_ C_R_

Children: Ellen: C_R_
Dan: ccR_
Anne: C_rr
Peter: ccrr
a. Must be heterozygous for dominant traits to have homozygous recessive children.
b. Elizabeth’s father: ccR_, mother C_rr
Mom must have been heterozygous for C, can’t determine dad’s genotype for nose line from this information alone.
c. John’s father: ccR_, mother C_R_
Cannot determine mom’s genotype for nose line from this info alone; one parent would have had to be heterozygous for tongue rolling.