Answer:
alleles of a gene separate from each other during meiosis.
Step-by-step explanation:
Mendel observed that the F1 expressed only one of the alternative variants (in this case, only rounded seeds appeared), while the other variant (wrinkle) disappeared. Mendel named "dominant" the expressed variant. Mendel allowed auto pollination and observed that in the second generation, F2, the other disappeared variant reappeared. Both alternative variants were present in the F2. Mendel named "recessive" the second alternative variant.
Mendel thought that hereditary traits determined by discrete factors were the possible explication for these phenotypes. These factors should have been present in the F1 in pairs. One of them came from one parental plant, and the other factor came from the other plant. These factors then separated again when sex cells were produced, giving two types of gametes, each with only one factor.
Mendel concluded that each individual (plant) has a pair of factors (alleles), one for each trait (R and r) and that the pair separates (segregates) during the formation of the gametes. This conclusion is known as the segregation principle (First Mendels´ Low).