Question

What properties of the bacteriophages made them ideal material for solving the controversy that which is the genetic material, protein or DNA?

Answer 1

T2 bacteriophages are simple, well‑separated two‑part particles that (1) inject only their genetic material into bacteria and (2) can be differentially and specifically labelled (protein vs DNA). They made a clean experimental system to test whether protein or DNA carries heredity.

There are reasons why that worked:

• Structural simplicity: a phage has just a protein exterior (head, tail) and a DNA molecule confined in the head, with no other complicated cellular components to confuse results.
• Physical separation of components: the genetic material (DNA) is inside the head while most proteins are external, so what enters the bacterium can be distinguished from the coat.
• Differential chemical labels possible: proteins contain sulfur (but not phosphorus) and DNA contains phosphorus (but not sulfur), so proteins could be labelled with 35S and DNA with 32P and then tracked.
• Clear infection behaviour: the phage attaches and injects its genetic material into the bacterium, so any label found inside the cell is the material responsible for takeover and progeny production.
• Experimental convenience: a short life cycle, high progeny yield, and the ability to physically separate phage coats from bacterial cells (e.g., by blending) made the results easy to observe and interpret.

These properties are exactly what allowed Hershey and Chase to show that DNA, not protein, is the hereditary material.