Exploring a Novel Genetic Interaction—Intergenic or Non-Allelic Interaction: The Case of Blood Groups and the Bombay Phenotype

A Study by Harshita Motvani, Medical Enthusiast, Batch 2025-2026

🧠✨ Classroom Discovery Highlight:
This insightful genetic analysis was born from an engaging classroom discussion, where curiosity sparked collaboration. The discovery highlights the true value of attentiveness in academic settings. Harshita Motvani’s contribution is a testament to how interactive learning can inspire original thought, deepen understanding, and lead to meaningful breakthroughs.

Genetic Cross: HH Iᴬi × hh Iᴬi

Interspecific Interaction:

It refers to the interaction between different genes located at different loci, influencing a single trait. These genes can affect the expression of each other in various ways.

Epistasis:

Epistasis is a form of gene interaction where one gene masks or modifies the expression of another gene at a different locus. In this case, the H gene is epistatic to the ABO gene — if hh genotype is present, it prevents the expression of the ABO alleles, resulting in the Bombay phenotype.

Punnett Square (F₂ Generation):

×	HIᴬ	Hi	hIᴬ	hi
HIᴬ	HH IᴬIᴬ A	HH Iᴬi A	Hh IᴬIᴬ A	Hh Iᴬi A
Hi	HH Iᴬi A	HH ii O	Hh Iᴬi A	Hh ii O
hIᴬ	Hh IᴬIᴬ A	Hh Iᴬi A	hh IᴬIᴬ Bombay	hh Iᴬi Bombay
hi	Hh Iᴬi A	Hh ii O	hh Iᴬi Bombay	hh ii Bombay

Phenotypic Ratio:
9 A : 3 O : 4 Bombay → 12 Normal : 4 Bombay (3:1)