Recurrent mutation and genome evolution: example of Sugary 1 and the origin of sweet maize

In maize (Zea mays L.), mutations at the Sugary 1 locus are the genetic bases far maize with specially uses cultivated throughout the western hemisphere precontact (pre-Columbian). The traditional North American sweet maize is homozygous for a recessive sugaryl (su1) allele. Determining the number of unique alleles among su1 maize races is relevant to the debate in archeology and evolutionary biology over whether independent mutation or migration plays a dominant role in the spread of novel phenotypes. We sequenced su1 from 57 cultivars of su1 maize and determined that five independent mutations have been selected. Three of these five alleles were single base pair changes at highly conserved sites and a fourth was a 1.3-kbp transposon. It will be interesting to note if future study in a variety of disciplines will lead to consensus on the significant role of recurrent mutation in evolution.