Question

RR ( Red) Antirrhinum/Snapdragon is crossed with white (WW) one. Offspring RW are pink. This is an example of
A. Dominant-recessive
B. Incomplete dominance
C. Hybrid
D. Supplementary genes

Answer 1

Hint: When an intermediate phenotype is observed in F1 generation, it means that neither of the parental alleles is dominant over the other.

Complete Answer:
When the Red flowered (RR) plant is crossed with a white (WW) one, in F1 pink colours are observed.

	W	W
R	RW	RW
R	RW	RW

F1 generation : RW (PINK)

Let us analyse the options to find the correct answer.
- Option A: None of the alleles is masking the expression of others i.e is dominant and neither one is getting masked i.e is recessive. Hence, this is an incorrect option.
- Option B: This is the case of incomplete dominance or partial dominance because neither of the alleles is dominant over the other. A heterozygote is obtained which expresses an intermediate phenotype compared to the parental phenotype. Hence, this is the correct option.
- Option C: A hybrid is an offspring obtained from cross between species which are not genetically alike. The parent plant or animal species can be of different species. Hence, this is an incorrect option.
- Option D: In case of supplementary genes the trait is contributed by both of the genes but the effect of one gene is masked by another. Hence, this is an incorrect option.

Thus, the correct answer is Option B) Incomplete dominance.

Additional Information: In incomplete dominance the resulting trait of the offspring is a blend of both the parental alleles and hence an intermediate phenotype is visible.

Note: If the F1 flowers are allowed to self fertilize the same genotypic and phenotypic ratio of 1:2:1 is obtained i.e red: pink: white. This implies that the red coloured gene is not completely dominant over the white coloured one.