Question

In a flowering plant, a cross is made between a homozygous dominant tall plant (TT) and a homozygous recessive dwarf plant (tt). What is the phenotypic ratio of the F1 generation?

• A. 1 Tall : 1 Dwarf
• B. 3 Tall : 1 Dwarf
• C. All Tall
• D. All Dwarf

Hint:

In a monohybrid cross between two homozygous parents (one dominant, one recessive), the F1 generation will always be heterozygous and express the dominant trait. The phenotypic variation appears in the F2 generation after self-crossing.

Answer 1

The Correct Option is C

The height of the plant is determined by a single gene with two alleles: \( T \) (dominant, tall) and \( t \) (recessive, dwarf). A homozygous dominant tall plant has the genotype \( TT \), and a homozygous recessive dwarf plant has the genotype \( tt \).
To determine the phenotypic ratio of the F1 generation, we perform a cross between the two plants using a Punnett square.
The \( TT \) parent can only produce gametes with the \( T \) allele, and the \( tt \) parent can only produce gametes with the \( t \) allele. The Punnett square for the cross is:
\[ \begin{array}{c|cc} & T & T
\hline t & Tt & Tt
t & Tt & Tt
\end{array} \] All offspring in the F1 generation have the genotype \( Tt \). Since the \( T \) allele is dominant, all plants with the \( Tt \) genotype will exhibit the tall phenotype.
Thus, the phenotypic ratio of the F1 generation is all tall (100% tall).