When a clock gene is switched on, it directs the cell to produce proteins, which eventually trigger a signal that switches the gene off.

BBC: Body clock 'set before birth'

The scientists used tests on mice to determine whether a defect in this gene is enough to trigger DCM.

BBC: Gene link to inherited heart disease

When it is time to make the plants male again, researchers spray on a chemical (which might also prove a money-spinner for the company) to trigger the activity of another foreign gene that blocks the activity of ribonuclease and allows pollen production once more.

ECONOMIST: Terminator genes

This will be done by adding extra copies of the gene using a mouse leukaemia virus modified to ensure it does not trigger cancer.

BBC: 'Brain cell transplant' for Alzheimer's

For example, Zeneca has managed to switch the bt gene, which gives maize plants resistance to nasty insects, on and off using another chemical trigger.

ECONOMIST: Terminator genes