Question

Work out separate monohybrid crosses up to F₂ generation between two pea plants and two Antirrhinum plants, both having contrasting traits with respect to the colour of the flower. Comment on the patterns of inheritance in the crosses carried out in such two cases.

Answer 1

Let’s consider the contrasting traits of flower colour in pea plants. The two parental plants are Purple (P) and White (p) flowers. The cross involves the genotype Pp (heterozygous purple) and Pp (heterozygous purple).

F₁ Generation:

Pp × Pp produces offspring with the following genotypes:

- PP (Purple): 25%

- Pp (Purple): 50%

- pp (White): 25%

F₂ Generation:

The F₂ generation has a phenotypic ratio of 3 : 1, with 3 purple and 1 white. This follows the Mendelian inheritance pattern of dominant and recessive traits.

Monohybrid Cross in Antirrhinum Plants:

Antirrhinum plants (Snapdragon) exhibit a different inheritance pattern. The colour of the flowers follows incomplete dominance, where red (R) is incompletely dominant over white (r).

F₁ Generation:

Rr × Rr produces offspring with the following genotypes:

- RR (Red): 25%

- Rr (Pink): 50%

- rr (White): 25%

F₂ Generation:

The F₂ generation exhibits a phenotypic ratio of 1 : 2 : 1

- 25% Red flowers (RR)

- 50% Pink flowers (Rr)

- 25% White flowers (rr)

This shows incomplete dominance, where the heterozygous condition results in an intermediate phenotype.