Question
Question: A red four o’clock flower (RR) is crossed with a white four o’clock flower (WW) and the resulting F1...
A red four o’clock flower (RR) is crossed with a white four o’clock flower (WW) and the resulting F1 offspring are all pink (RW). If two of the pink offsprings are crossed, what proportion of genotype would you expect to see in F2 generation?
A) 1RW:2RR:1WW
B) 2RR:1RW:1WW
C) 1RR:2RW:1WW
D) 4RR:0RW:0WW
E) 2RR:0RW:2WW
Solution
-This question is related to deviation of Mendel’s law of dominance. It actually shows incomplete dominance where the offspring has a totally different phenotype.
Complete answer:
The offspring produced in F1 generation have a totally different phenotype (pink flowers) as compared to their parents who were red and white. This is actually known as incomplete dominance. When a cross is made between F1-hybrids via self-fertilization, both parental phenotypes i.e. the red colour and white colour reappear in the individuals of F2 generation.
The cross can be explained by following diagram-
The phenotype and genotype of F2 generations will be-
| Genotype | RW | RW | WW |
|---|---|---|---|
| Genotype ratio | 1 | 2 | 1 |
| Phenotype | Red | Pink | White |
| Phenotype ratio | 1 | 2 | 1 |
Thus, the correct answer is- C. 1RR:2RW:1WW.
Note: Although incomplete dominance is a deviation of law of dominance, it only deviates from law of dominance. It follows the remaining two laws which are the law of independent assortment and law of segregation.