A cross between two plants resulted in the formation of tall and...

A phenotypic ratio of $3:1$ for tall and dwarf offsprings is obtained in a monohybrid cross when both parents are heterozygous for the trait.

Let the dominant allele for tallness be $T$ and the recessive allele for dwarfness be $t$.

When two heterozygous parents (Tt$) are crossed (Tt \times Tt$), the gametes produced by each parent are $T$ and $t$.

The resulting offspring genotypes are $1TT$ : $2Tt$ : $1tt$.

The corresponding phenotypes are $3$ tall (TT$and$Tt$) and 1$ dwarf (tt$).<br><br>Thus, the genotypes of the parents must be$Tt$and$Tt$.<br><br>Answer: Tt and Tt$