Question

"Mendel knew that the allele for smooth (R) seeds was dominant over the allele for wrinkled (r) seeds. If this cross was Rr × rr, what numbers would fill the middle column"

Answer 1

Rr and rr in the ratio of 1:1

Explanation:

If allele for smooth seed is Dominant over the allele for wrinkled seeds, and they are crossed 50 per-cent of the progeny will be heterozygous dominant  and 50 per-cent will be homozygous recessive.

Rr  X  rr

Rr Rr rr rr  F1 generation.

     r      r

R    rR   rr

r     Rr   rr

From Punnet square it will be 50 per-cent  chance each of rr and Rr.