Here's why:
* Mendel's Law of Dominance: This law states that when two contrasting alleles for a trait are present, only one (the dominant allele) is expressed, while the other (the recessive allele) is masked.
* F1 Generation: When Mendel crossed pure-breeding pea plants with contrasting traits (e.g., tall vs. short), all the F1 offspring inherited one dominant allele and one recessive allele. Since the dominant allele masks the recessive allele, the F1 plants all displayed the dominant trait (e.g., tallness).
Important Note: The recessive allele doesn't disappear entirely; it's simply not expressed in the F1 generation. It can reappear in the F2 generation when the F1 plants self-pollinate.
