Question

in a plant flower colour is the example of quantitative trait and controlled by one gene pair . how many plants show parental phenotype in F2 generation

Answer 1

1/2

Answer 2

The question states that flower color is a "quantitative trait" controlled by "one gene pair". This phrasing is key.

1. Quantitative Trait: Typically, quantitative traits show continuous variation and are controlled by multiple genes (polygenic inheritance). However, if controlled by "one gene pair," it implies that the trait exhibits more than two distinct phenotypes, which is characteristic of incomplete dominance or codominance. In such cases, the heterozygote has an intermediate phenotype, creating a range of phenotypes that can be considered quantitative in a simplified sense.
2. Controlled by one gene pair: This limits the genetic control to a single gene with two alleles.

Considering these two points, the most appropriate genetic model is incomplete dominance.

Let's assume the two alleles for flower color are R (for Red) and r (for White). Under incomplete dominance:

• RR: Red flowers (one parental phenotype)
• rr: White flowers (the other parental phenotype)
• Rr: Pink flowers (intermediate phenotype)

Cross between true-breeding parents (P generation): Parental Cross: Red (RR) × White (rr)

F1 Generation: All F1 offspring will have the genotype Rr and phenotype Pink. At this stage, no plants show the parental phenotypes (Red or White).

F2 Generation (by self-pollinating F1 plants): Cross: Rr × Rr

Using a Punnett Square:

Gametes	R	r
R	RR	Rr
r	Rr	rr

Genotypic Ratio in F2: 1 RR : 2 Rr : 1 rr Phenotypic Ratio in F2: 1 Red : 2 Pink : 1 White

Identifying Parental Phenotypes in F2: The parental phenotypes are Red (RR) and White (rr).

• The proportion of Red (RR) plants in F2 is 1/4.
• The proportion of White (rr) plants in F2 is 1/4.

Total proportion of plants showing parental phenotypes in F2: (1/4) [Red] + (1/4) [White] = 2/4 = 1/2

Therefore, 1/2 or 50% of the plants in the F2 generation will show parental phenotypes.