Question

Why did short plants reappear in mendel’s F2 generation?

Answer 1

Answer:

Because the F1 plants all had a lowercase a/short plant allele, there was a 25% chance that two plants would contribute it to their offspring and they both did sometimes to make a aa offpsring.

Explanation:

All the F1 plants were heterozygous, so when they were crossed, the resulting genotypic ratio was 1 AA : 2 Aa : 1 aa.  As you can see, this is the first time since the parent generation that there is a aa genotype and short plant phenotype, so that's why short plants reappeared.