Question

When a purebred, red flower -producing plant of genotype RR is crossed with purebred , white flowers-producing plant of genotype rr, all the F1​ plants produced pink flowers If all the plant in each generation from F1​ to F6​ are selfed, what will be the percentage of plants with red and white flowers in the final population of plants with red and white flowers in the final population consisting of a large number of individuals? (Consider that flower color has no effect on reproduction and survival.)
A. $3−4$
B. $12−13$
C. $49−50$
D. $97−100$

Answer 1

Hint: RED Flower $\times$ WHITE Flower $\rightarrow$ PINK Flower. This is a case of incomplete dominance, only homologous plants show the character of parents. So, we can solve it by calculating the no. of homozygous individuals.

	R	r
R	RR	Rr
r	Rr	rr

Complete answer:
In this question it is given that the crossing of a red flowered plant and a white flowered plant produces all the offspring with pink flowers which is a blend of red and white. This occurs due to the blending of both the alleles which is called incomplete dominance. So, heterozygous individuals are pink and homozygous individuals are red or white. Now, we have asked what will be the percentage of red and white flowers, when f1 to f6 are selfed.

As we already mentioned we can calculate it by calculating the percentage of homozygous individuals. There is a relationship between phenotypic character of F1 and F6 generation that F6 mimics the F1 generation because the pink flowers on fertilization will produce red:pink:white flowers in the ratio of $1:2:1$. So, the percentage of red and white flowers in F6 generation will be:

$1 white + 1 red : 4 \text{total plant}$ $=\dfrac{2}{4} \times 100 = 50\%$.

Hence, The correct answer is option (C).

Note: We can also solve it by calculating percentage of homologous plants $:$ genotype in F1 generation: RR, Rr, rR, rr.
$\%$ of homologous plants $= \dfrac{2}{4} \times 100 = 50\%$.
So, the ratio will be $50:50$ or $49:50$.