Question

People who have Tay-Sachs disease cannot metabolize some lipids effectively. Tay-Sachs is a recessive disorder. A student used a Punnet Square to determine the probability of offspring inheriting the disease. The results from a Punnet Square are 25% TT, 50% Tt, and 25% tt.

Which conclusion can be made regarding the phenotype of the parents based on these results?

The parents must be TT, Tt

The parents must be Tt, tt

The parents must be TT, tt

The parents must be Tt, Tt

Answer 1

The parents must be Tt, Tt

Step-by-step explanation:

Based on these results, we can conclude that each of the parents will have one dominant (T) and one recessive allele (t). We can prove this by drawing the Punnett square:

T t

T TT Tt

t Tt tt

We can see that the offspring will have the Tt genotype in two cases, the TT genotype in one case, and the tt genotype in one case, as well. Now we need to do some basic math. Two out of four is 50% (Tt - 50%), and one out of four is 25% (TT - 25%, tt - 25%).

This means that the parents must be Tt, Tt.