Final answer:
The offspring of the P1 generation are called the F1 generation, which stands for the first filial generation, where dominant traits were observed in Mendel's experiments with peas.
Step-by-step explanation:
The offspring of the P1 generation are known as the F1 generation. When Gregor Mendel conducted his foundational experiments in genetics, he crossed different varieties of pea plants and labeled the original plants as the P (parental) generation. The outcome of these crosses, the first generation of offspring, was referred to as the F1 (first filial) generation. It is in the F1 generation where Mendel observed the manifestation of dominant traits, such as purple flowers, with the recessive traits, like white flowers, seemingly disappearing. However, when F1 plants were allowed to self-pollinate, their offspring, the F2 generation, clearly demonstrated a mixture of dominant and recessive traits, indicating that the recessive traits had not disappeared but were simply hidden in the F1 generation.