Q82. The genome of a bacterium encodes for 10 different surface antigens, whose
expression can be turned ‘ON’ or ‘OFF’ randomly and independently. The
number of possible antigenic combinations is__________.

Problem Breakdown

The bacterium’s genome encodes 10 different surface antigens, each with independent ON or OFF expression. This setup models phase variation in bacteria, where random switching generates diverse antigenic profiles to evade host immunity.

Each antigen has 2 states: expressed (ON) or not (OFF). With independent control, total combinations equal 2¹⁰.

Step-by-Step Solution

One antigen: 2 possibilities (ON, OFF).

Two antigens: 4 combinations (ON-ON, ON-OFF, OFF-ON, OFF-OFF).

Pattern: For n antigens, 2ⁿ total states.

Here, n=10, so 2¹⁰ = 1024.

No restrictions like mutual exclusivity apply; independence confirms all subsets possible.

The bacterium genome encoding 10 surface antigens, with expression switched ON or OFF randomly and independently, highlights phase variation in microbiology. This mechanism allows pathogens to produce 1024 possible antigenic combinations, crucial for evading immune responses in competitive exams like CSIR NET.

Biological Context

Phase variation involves reversible ON/OFF switching of surface structures via slipped-strand mispairing or recombination. In this model, each antigen acts as a binary switch, enabling population diversity without genetic mutation.

Calculation Details

Binary states per antigen: 2 (ON or OFF).

Independent expression: Multiplicative total, 2 × 2 × ⋯ = 2¹⁰.

Result: 1024 unique profiles, from all OFF to all ON.

Exam Relevance

CSIR NET questions test combinatorial logic in antigenic variation, distinguishing from gene conversion models. No options listed, but common distractors include 10 (only ON), 20 (ON+OFF), or 10² (512, incorrect base).

Keywords

Bacterium genome, surface antigens, antigenic combinations, phase variation, CSIR NET life