25) E

Let the dominant allele be: **T**

Let the recessive allele be : **t**

If only U has a recessive condition, their genotype must be **tt**. This means that S and T must be heterozygous.

Since we want the minimum number of heterozygous people, we must assume that R has to be **TT**.

In order for S to be **Tt** and R to be **TT**, only one of P and Q needs to heterozygous.

This means that if only U has the recessive people, 3 people must be heterozygous.

If R and U both have the recessive condition, P and Q must both be heterozygous.

This means that if R and U have the recessive condition, 4 people (P, Q, S and T) must be heterozygous. Hence, E is the answer.