Question

State Mendel’s Law of Dominance and explain it with a monohybrid cross.

Hint:

Dominant trait appears in F\(_1\), Recessive trait hides but reappears in F\(_2\). Monohybrid cross shows 3:1 phenotypic ratio.

Answer 1

Concept: Mendel’s Law of Dominance is one of the fundamental principles of heredity proposed by Gregor Mendel. It explains how traits are expressed when two contrasting alleles are present in an organism. Statement of Mendel’s Law of Dominance: When two contrasting traits are present in an organism, only one trait is expressed in the F\(_1\) generation. The expressed trait is called the dominant trait, while the suppressed trait is called the recessive trait. Explanation using Monohybrid Cross: A monohybrid cross involves the inheritance of a single pair of contrasting characters. Example: Height in pea plants

• Tall plant (TT) — Dominant
• Dwarf plant (tt) — Recessive

Parental Generation (P): \[ \text{TT (Tall)} \times \text{tt (Dwarf)} \] Gametes formed: \[ T, T \quad \text{and} \quad t, t \] F\(_1\) Generation: \[ Tt, Tt, Tt, Tt \] All offspring are tall because the dominant allele (T) masks the recessive allele (t). F\(_2\) Generation (Selfing F\(_1\)): \[ Tt \times Tt \] Punnett Square: \[ \begin{array}{c|cc} & T & t
\hline T & TT & Tt \\ t & Tt & tt \\ \end{array} \] Results:

• Genotypic ratio: 1 TT : 2 Tt : 1 tt
• Phenotypic ratio: 3 Tall : 1 Dwarf

The appearance of dwarf plants in F\(_2\) shows that the recessive trait was present but masked in F\(_1\). Conclusion: Mendel’s Law of Dominance states that in a pair of contrasting traits, only the dominant trait is expressed in the F\(_1\) generation, while the recessive trait remains hidden but reappears in the F\(_2\) generation.