Biology Inheritance / Variation & Genetics BUMHS 2022
PMDC Verified Question 52 of 94
When two or more genes interact in a way that their effect is additive expression, it is:
A
Co-dominance relation
B
Phylogenetic inheritance
C
Epistasis
D
Incomplete dominance
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: Incomplete dominance
Concept:

Gene interactions can produce non-Mendelian phenotypic ratios depending on how alleles mask or blend with each other.

Solution:

  • In incomplete dominance, the effects of two alleles are blended, and their expression results in an intermediate phenotype.
  • This often shows an additive effect (where the dosage of the functional allele dictates the intensity of the phenotype, such as pink flowers from red and white parents).
  • Note: While polygenic inheritance is the classic example of additive gene effects across multiple loci, based on the provided exam key, incomplete dominance acts additively at a single locus.


Why other options are incorrect:

  • Co-dominance: Both alleles are fully and distinctly expressed without blending (e.g., AB blood group).
  • Epistasis: One gene locus completely masks or modifies the expression of a second, different gene locus.
  • Phylogenetic inheritance: A likely typographical error in the original exam for 'Polygenic inheritance'.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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