Question

When a pure breed, red flower producing plant of genotype RR is crossed with a pure breed, white flower producing plant of genotype rr, all the $F_1$ plants produce pink flowers. If all the plants in each generation from $F_1$ to $F_6$ are selfed, what will be the percentage of the plants with red and white flowers in the final population consisting of a large number of the population?(Consider that flower color has no effect on reproduction and survival).
A. 3 - 4
B. 12 - 13
C. 49 - 51
D. 97 - 100

Answer 1

Hint: Through a series of experiments, Mendel proposed that the genes or characteristics are inherited from one generation to the other as pairs of alleles that behave in a recessive or dominant pattern. The $F_1$ plants are usually produced by cross pollination or hand pollination. The $F_1$ generation plants are selfed to produce $F_2$ generation plants.

Complete Answer:
- When purebred red flowering plants (RR) are crossed with purebred white flowering plants (rr), in the first filial ($F_1$) generation, the plants produce pink flowers (Rr).
- It is an intermediate expression. When these $F_1$ plants undergo self fertilization, the plants produced in $F_2$ generation also show the same deviation.
- Red, pink and white flowers are produced in the phenotypic ratio of 1:2:1.
- On fertilization, pink flowers produce red : pink : white flowers in the ratio of 1:2:1 even if the crosses are done for ‘N’ generations.

The different types of plants produced are
Red flowered plants - 25%
Pink flowered plants - 50%
White flowered plants - 25%
Hence the total percentage of white and red flowers produced in $F_6$ generation is 50%.

	R	r
R	RR (red)	Rr (pink)
r	Rr (pink)	Rr (white)

Therefore the correct answer is C, 49% to 51%.

Note: The red colour is observed in homozygous dominant condition (RR). The white color is observed only in homozygous recessive conditions(Rr). But in case of heterozygous condition(Rr), the gene for red color fails to suppress the recessive gene (r) completely (except pea plant). As a result the intermediate condition with pink flowers is observed. This condition is known as incomplete dominance or partial dominance.