RNA cannot serve as hereditary material.

Once DNA was established as the hereditary material of cells, RNA was often assigned a secondary role: an intermediate that copied information from DNA and helped express it.

Tobacco mosaic virus provided a direct test of whether that hierarchy was universal. The virus consists largely of RNA wrapped in a protein coat, and researchers could separate the components experimentally.

Reconstituted virus containing the RNA became infectious again. More importantly, experiments using components from different viral strains showed that inherited viral characteristics followed the RNA, not the protein coat.

RNA could therefore function as a genome.

Many viruses are now known to use RNA as their hereditary material, while cellular organisms use DNA for long-term genome storage.

The result does not make RNA and DNA interchangeable in every setting. Their chemical stability, replication, and repair differ substantially.

It also differs from the broader claim that RNA is “only a messenger.” RNA can serve hereditary, catalytic, regulatory, and structural roles; this card is specifically about its ability to carry genetic information across generations of a replicating system.