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

Plant height is controlled by a single gene with two alleles: \( T \) (dominant, tall) and \( t \) (recessive, dwarf). A homozygous dominant tall plant has genotype \( TT \), and a homozygous recessive dwarf plant has genotype \( tt \).
To determine the phenotypic ratio of the F1 generation, a cross between these two plants is performed using a Punnett square.
The \( TT \) parent produces only gametes with the \( T \) allele, and the \( tt \) parent produces only gametes with the \( t \) allele. The Punnett square for this cross is:
\[ \begin{array}{c|cc} & T & T \\ \hline t & Tt & Tt \\ t & Tt & Tt \\ \end{array} \] All F1 generation offspring have the genotype \( Tt \). Due to the dominance of the \( T \) allele, all plants with the \( Tt \) genotype will display the tall phenotype.
Consequently, the phenotypic ratio of the F1 generation is 100% tall.