CBSE · Class 10 · Science · HeredityExplain Gregor Johann Mendel's monohybrid cross experiment with the help of a suitable checker board (Punnett square). What conclusions were drawn from this experiment?

Introduction to Mendel's Monohybrid Cross\nGregor Johann Mendel, known as the Father of Genetics, performed hybridization experiments on garden pea plants (Pisum sativum). A monohybrid cross involves the inheritance of a single pair of contrasting characters, such as plant height (tall vs. dwarf).

Experimental Steps

1. Parental Generation (P): Mendel crossed a pure-breeding tall pea plant ($TT$) with a pure-breeding dwarf pea plant ($tt$).
2. First Filial Generation ($F_1$): All the plants obtained in the $F_1$ generation were tall ($Tt$). This showed that the trait for tallness is dominant, while dwarfism is recessive.
3. Self-Pollination of $F_1$: Mendel then self-pollinated the $F_1$ tall plants ($Tt \times Tt$) to raise the $F_2$ generation.

Punnett Square (Checker Board) for $F_2$ Generation\nTo determine the genotypes and phenotypes of the $F_2$ generation, a Punnett square is used:

Results and Ratios

• Phenotypic Ratio: 3 Tall : 1 Dwarf (75% tall, 25% dwarf).
• Genotypic Ratio: 1 $TT$ (pure tall) : 2 $Tt$ (hybrid tall) : 1 $tt$ (pure dwarf), i.e., $1:2:1$.

Conclusions Drawn

1. Law of Dominance: Out of a pair of contrasting factors, only one is able to express itself in the $F_1$ generation (dominant), while the other remains masked (recessive).
2. Law of Segregation (Law of Purity of Gametes): The alleles do not blend and separate/segregate from each other during gamete formation so that each gamete receives only one allele for each trait.