The limits of selection during maize domestication

The domestication of all major crop plants occurred during a brief period i n human history about 10,000 years ago(1). During this time, ancient agricu lturalists selected seed of preferred forms and culled out seed of undesira ble types to produce each subsequent generation. Consequently favoured alle les at genes controlling traits of interest increased in frequency, ultimat ely reaching fixation. When selection is strong, domestication has the pote ntial to drastically reduce genetic diversity in a crop. To understand the impact of selection during maize domestication, we examined nucleotide poly morphism in teosinte branched1, a gene involved in maize evolution(2). Here we show that the effects of selection were limited to the gene's regulator y region and cannot be detected in the protein-coding region. Although sele ction was apparently strong, high rates of recombination and a prolonged do mestication period probably limited its effects. Our results help to explai n why maize is such a variable crop. They also suggest that maize domestica tion required hundreds of years, and confirm precious evidence that maize w as domesticated from Balsas teosinte of southwestern Mexico.