Why did mendel prevent his plants from self-pollinating? so they couldn't produce offspring to insure that each plant's offspring would remain identical to the parents to control the crossing of the traits to maintain a pure strain

Suppose you have monohybrid pea plants in your garden and find that they produce round seed to wrinkled seeds in the ratio of 3: 1. if the allele are designated (r & r) receptively. what is the probable genotypes of the round seeds which produced f 1 ? rr & rr rr only rr & rr rr only rr only