Mendel in one of

Mendel crossbred round seed plants with wrinkled seed plants, it was observed that in F1 progeny, only round seed plants were obtained and no wrinkled seed plant was obtained. But in F2 generation, both round and wrinkled seed plants were obtained in 3:1 ratio. Since, in F1 progeny, only round seeds were obtained so, dominant trait was round seed and recessive trait was wrinkled seeds.