Question

A cross between black-flowered plant and white-flowered plant yielded grey flowered
plants. The phenomenon is ……………………..
A) Codominance
B) Pseudodominance
C) Incomplete dominance
D) Epistasis

Answer 1

Hint:-The phenotype depends on the dominant allele. The dominant allele expresses itself while the recessive allele remains unexpressed. This is the phenomenon of dominance. Co-dominance is the phenomenon in which both the alleles express themselves. In incomplete dominance, the dominant allele expresses itself but not completely.


Complete Answer:-
The black flower is a dominant character. The white flower is recessive. For a plant to bear white flowers it should have both the recessive alleles. Whereas, it will bear black flowers if it has both the dominant alleles. When this plant bears grey flowers, it means that the allele for the black colour is not completely dominant over the allele for the white colour which results in grey colour. This phenomenon is known as incomplete dominance. Black is incompletely dominant over white.
The phenotypes and genotypes of black white and grey Flowers are as follows :
Black – BB
White- bb
Grey- Bb
Thus, in heterogeneous form, this plant will produce grey flowers. Instead of black and white. Let us consider,

	B	B
b	Bb	Bb
b	Bb	Bb

All the progenies are heterogeneous. Thus a cross between a black flowered and a white-flowered plant results in a grey flowered plant.
Thus, the right option is C.

Note:- An example of incomplete dominance in humans is the Tay Sachs disease. In incomplete dominance, the characters of both the parent’s blend, thus it is also called the ‘blending inheritance’. It forms a new character which is present in neither of the parents. Incomplete dominance does not follow Mendelian rules of dominance.