In efflux, a resistance gene encodes a membrane protein that actively pumps tetracycline out of the cell.

The earliest single resistance gene was identified as effective against yellow rust.

As a result, the resistance gene frequency in the population would remain low.

The use of a single resistance gene against various pests and diseases plays a major role in resistance breeding for cultivated crops.

These resistance genes, however, became ineffective due to the acquisition of virulence to that particular resistance gene rendering the variety susceptible.