Question

A cross between a pure-bred plant with red flowers and a pure-bred plant with white flowers produced F1 generation with pink flowers. If the plants with pink flowers are selfed, what is the proportion of white : pink : red flowers expected in the next generation?

• A. 1 : 1 : 1
• B. 1 : 2 : 1
• C. 2 : 1 : 2
• D. 2 : 2 : 1

Hint:

In incomplete dominance, the self-cross of F1 heterozygotes (RW) will result in a 1:2:1 phenotypic ratio in the F2 generation.

Answer 1

The Correct Option is B

Step 1: Understanding incomplete dominance.
In this case, the plants with red flowers (RR) and white flowers (WW) are crossed. The F1 generation will have pink flowers (RW), which is a classic example of incomplete dominance. Incomplete dominance occurs when neither allele is completely dominant, resulting in an intermediate phenotype (pink flowers, in this case). The genotype of the F1 generation will be heterozygous (RW).

Step 2: Self-crossing of F1 plants.
When the F1 plants (RW) are selfed, the offspring will inherit one allele from each parent. The possible combinations of alleles are: - RR (red flowers)
- RW (pink flowers)
- WW (white flowers)
The expected genotypic ratio from a self-cross between two heterozygotes (RW × RW) is: \[ \text{Genotypic ratio:} \ 1 \, \text{RR} : 2 \, \text{RW} : 1 \, \text{WW}. \] Thus, the expected phenotypic ratio is 1 red : 2 pink : 1 white.
Step 3: Conclusion.
The proportion of white : pink : red flowers in the next generation will be 1 : 2 : 1, corresponding to option (B).