In pea plants, tallness (T) is dominant over dwarfness (t). Two heterozygous tall plants were crossed. a. State the genotypes of the parents. b. Draw a genetic diagram to show the cross. c. Determine the genotypic ratio of the offspring. d. Determine the phenotypic ratio of the offspring.

Tallness (T) is dominant over dwarfness (t).
Two heterozygous tall plants were crossed.

Since tallness (T) is dominant and the plants are heterozygous, they must carry one dominant allele and one recessive allele.
The genotype of each parent is $\boxed{Tt}$.

• Parents (P): $Tt \times Tt$
• Gametes: $T, t$ from each parent

• $TT$: 1
• $Tt$: 2
• $tt$: 1

The genotypic ratio is $\boxed{1 TT : 2 Tt : 1 tt}$.

• $TT$: Tall
• $Tt$: Tall (since T is dominant)
• $tt$: Dwarf

• Tall: $1 (TT) + 2 (Tt) = 3$
• Dwarf: $1 (tt) = 1$

The phenotypic ratio is $\boxed{3 \text{ Tall} : 1 \text{ Dwarf}}$.