In garden pea, the gene T for tall is dominant over its allele for dwarf. Give the genotypes of the parents in the following crosses.

 A. Tall × Dwarf producing all tall plants. 

B. Tall × Tall producing 3 tall and 1 dwarf plants.

A. As T is dominant over t. Therefore to produce all tall plants from a cross of tall plant with a dwarf plant is only possible when the tall plant is homozygous for the dominant allele. Therefore, the genotype should be  TT × tt.
B) As T is dominant over t. Therefore to produce 3 tall plants and 1 dwarf plant from a cross of tall plant with another tall plant is only possible when the tall plant is homozygous for the dominant allele. Therefore, the genotype should be Tt × Tt.