Question

(a) A garden pea plant bearing terminal, violet flowers when crossed with another pea plant bearing axial, violet flowers, produced axial, violet flower and axial, white flowers in the ratio of 3:1. Work out the cross showing the genotypes of the parent pea plants and their progeny.
(b)Name and state the law that can be derived from this cross and not from a monohybrid cross.

Answer 1

Hint: In a pea plant, the violet flowers are dominant and white flowers are recessive and the axial position of the flower is dominant and the terminal position is the recessive position.

Complete answer:
(a) The cross between pea plant bearing terminal, violet flowers and pea plant bearing axial, violet flowers, produces axial, violet flower and axial, white flowers in the ratio of 3:1 (Phenotypic ratio).

Consider;
T: Violet flower (Dominant)
t: White flower (Recessive)
P: Axial position (Dominant)
p: Terminal position (Recessive)

According to the question, the cross produces axial violet and axial white flowers, so the genotype of parent plants must be terminal violet flowers (ttPp) and axial white flowers (TtPp).

The cross can be represented as
Parents: ttPp × TtPp
Gametes: tP, tp × TP, Tp, tP, tp

Gametes	tP	tp
TP	TtPPAxial purple flower.	TtPpAxial purple flower.
Tp	TtPpAxial purple flower.	TtppAxial white flower.
tP	ttPPTerminal purple flower.	ttPpTerminal purple flower.
tp	ttPpTerminal purple flower.	ttppTerminal white flower.

(b) The law followed by the above cross is the law of independent assortment according to which two pairs of characters/traits are involved in a cross, one pair of traits segregates independently of the other pair of characters. This law cannot be shown by monohybrid cross because it involves only one pair of traits.

Note: 1)Mendelian inheritance can be described by three mendelian laws that are the law of dominance, the law of segregation, and the law of independent assortment.
2)Mendel selected seven pairs of contrasting characters of pea plant for his experiments and the reason why Mendel selected pea plant was because of the shorter life cycle of the pea plant, its small size, bisexual flowers, and self-pollinating nature.