The genetic changes - so far largely unknown - between the two varieties have been brought out through DNA study, according to a Los Angeles Times report.

Scientists analysed the DNA sequences of 774 genes in strains of teosinte - a wild grass, from which corn was domesticated 6,000 to 9,000 years ago in Mexico  - and estimated that about two to four percent of the plant's genome contributed to the domestication of corn.

A small group of genes were alike in all corn strains, but were far more varied in teosinte strains. Learning what these selected genes do should help in breeding better varieties, Brandon Gaut, lead author on the study, was quoted as saying by the Los Angeles Times.

In some respects, teosinte is corn-like - it has the same thin leaves and pollen-producing tassels. Some of the genes, known to be involved in responding to plant growth hormones or in making amino acids, differ somewhat between ears of teosinte and corn.

The ears are very different in corn and teosinte. The latter has side branches covered with many ears, each consisting of a single row of hard, triangular seeds.

Corn has lost those side branches. Multiple single-rowed ears have fused together to form fat cobs of fleshy seeds. One gene - dubbed tb1 - is known to be part of this change. It suppresses branching in corn.