Question

what was mendels explanation for his observation that traits that had disappeared in the f1 generation reappeared in the f2 generation of the pea plants he used in his experiments?
traits can be dominant or recessive, and the recessive traits were \hidden\ by the dominant ones in the f1.
the mechanism controlling the appearance of traits was different between the f1 and the f2
new mutations were frequently generated in the f2 progeny,
einventing\ traits that had been lost in the f1.
the traits were lost in the f1 due to dominance of the parental traits.

Explanation:

Mendel proposed that traits have dominant and recessive forms. In the F1 generation, the recessive trait is "hidden" (not expressed) because the dominant trait masks it. But in the F2 generation, when the F1 plants self - pollinate (or cross - pollinate in relevant cases), the recessive trait can reappear. This is based on his law of segregation.

Answer:

Traits can be dominant or recessive, and the recessive traits were "hidden" by the dominant ones in the F1.