As in animals, plant genes are located on tiny packages of DNA in the nucleus of every cell, called chromosomes. Whereas human chromosomes come in matched pairs, clovers have four copies of each chromosome per cell. The gene responsible for four-leaf clovers is ‘recessive’, which means that the plant will only produce four leaves if it has the four-leaf gene on all four chromosomes, which is a rare occurrence.
Even then, environmental conditions such as temperature and soil acidity will also have an impact on whether the four leaves develop. A 2017 survey concluded that around 1 in 5,000 clovers is four-leaved, but they do tend to be found in clusters.