R rr Rr RR
I gave my students this multiple choice question: The ability to roll the tongue in humans is coded by the dominant allele R. The inability to roll the tongue is coded by the recessive allele r. A man with an RR allele combination for the trait produces a zygote with a woman with an rr allele combination for the trait. Which allele combination could occur in the zygote?

Only one answer is correct among these 4 choices:
- R
- rr
- Rr
- RR

Could you tell me which one is correct?

Rr