In this dihybrid cross, we have two double heterozygous parents. Parent 1 (PpRr; Purple flowers, a Round seeds) and prent 2 (PpRr; Purple flowers, a Round seeds), to obtain the possible gametes we must combine each allele as it follows:
As each parent is a double heterozygous the gamete combination will be the same, having four gametes (PR, Pr, pR, pr) for parent one and four gametes (PR, Pr, pR, pr) for parent2.
Parent plant 1
Gamete 1: PR
Gamete 2:Pr
Gamete 3:pR
Gamete 4:pr
Parent plant 2
Gamete 1:PR
Gamete 2:Pr
Gamete 3:pR
Gamete 4:pr