When Mendel crossed a set of “true-breeding” purple-flowered (PP) pea plants with a set of true-breeding white-flowered (pp) pea plants, he found that –

of the offspring had purple flowers. This result on its own showed that the purple flower trait was –
to the white flower trait, but to understand that the offspring carried one allele from each of the parents, he needed to –
.
cross the offspring with each otherrecessive3/4cross the offspring with the true-breeding purple-flowered parentPPalldominantneutraldissect the flowerspphalf

3/4; dominant; cross the offspring with each other