When both alleles express their effect on being present together, the phenomenon is called

The correct option is B Codominance

A.Dominance – In a pair of contrasting characters, one character is expressed, and another one is not expressed. Expressed character is called dominant character and not expressed character is called recessive character.

B.Codominance – Expression of phenotypes of both parents in progeny is called Codominance.

C.Pseudodominance – The situation in which the inheritance of a recessive trait appears like a dominant pattern.

D.Amphidominance – no expression of this type of dominance.

So, the correct option is ‘codominance’.