Dominant allele is H
Recessive allele is h
The heterozygous plant is Hh and its phenotype is a tall plant.
If we cross two heterozygous
Parents: Hh x Hh
F1 generation: HH Hh Hh hh
Phenotype ratio is 3:1 (tall plants : short plants)
HH and Hh are for tall plants
hh is for short plants