Science - genes question?

The dominant allele is the round seeded pea plant because when the two were crossed, the resulting first generation plants were also all round seeded. Dominance simply means that the heterozygous offspring will exhibit that phenotype which is dominant, in this case: round seeded. If the first generation heterozygous offspring had been wrinkled-seeded, then that would be the dominant allele, but in this case it is not, it is the recessive allele.