In order to trace the inheritance of traits Mendel crossed pea plants having one contrasting character or a pair of contrasting characters. When he crossed pea plants having round and yellow seeds with pea plants having wrinkled and green seeds, he observed that no plants with wrinkled and green seeds were obtained in the $F_1$ generation. When the $F_1$ generation pea plants were cross-bred by self-pollination, the $F_2$ generation had seeds with different combinations of shape and colour also. (a) Write any two pairs of contrasting characteristics of pea plant used by Mendel other than those mentioned above. (b) Differentiate between dominant and recessive traits. (c) State the ratio of the combinations observed in the seeds of $F_2$ generation (in the above case). What do you interpret from this result? OR (c) Given below is a cross between a pure violet flowered pea plant (V) and a pure white flowered pea plant (v). Diagrammatically explain what type of progeny is obtained in $F_1$ generation and $F_2$ generation: Pure violet flowered plant $\times$ Pure white flowered plant (VV) (vv)

(a) Two pairs of contrasting characteristics of pea plants used by Mendel other than seed shape and seed colour:

1. Plant height: Tall vs. Short
2. Flower colour: Violet vs. White

(b) Difference between dominant and recessive traits:

• Dominant Trait: A trait that is expressed in the $F_1$ generation even when only a single copy of the gene controlling it is present (e.g., 'T' in 'Tt' makes the plant tall).
• Recessive Trait: A trait that is masked in the $F_1$ generation in the presence of a dominant allele, and is expressed only when both copies of the gene are identical and recessive (e.g., 't' in 'tt' makes the plant short).

(c) Ratio of combinations in $F_2$ generation and interpretation:

• Ratio: The phenotypic ratio of the combinations in the $F_2$ generation is $9:3:3:1$ (9 Round-Yellow : 3 Round-Green : 3 Wrinkled-Yellow : 1 Wrinkled-Green).
• Interpretation: This result shows that the seed shape (round/wrinkled) and seed colour (yellow/green) traits are inherited independently of each other. This is known as the law of independent assortment.

OR

(c) Diagrammatic explanation of the cross between pure violet (VV) and pure white (vv) flowered pea plants:

When a pure violet flowered plant ($VV$) is crossed with a pure white flowered plant ($vv$):

• In the $F_1$ generation, all progeny have the genotype $Vv$ and exhibit violet flowers because violet is the dominant trait.
• When $F_1$ plants ($Vv$) are self-pollinated, the $F_2$ generation produces violet and white flowered plants in a phenotypic ratio of $3:1$.