The limits of selection during maize domestication

Abstract

The domestication of all major crop plants occurred during a brief period in human history about 10,000 years ago. During this time, ancient agriculturalists selected seed of preferred forms and culled out seed of undesirable types to produce each subsequent generation. Consequently, favoured alleles at genes controlling traits of interest increased in frequency, ultimately reaching fixation. When selection is strong, domestication has the potential to drastically reduce genetic diversity in a crop. To understand the impact of selection during maize domestication, we examined nucleotide polymorphism in teosinte branched1, a gene involved in maize evolution. Here we show that the effects of selection were limited to the gene's regulatory region and cannot be detected in the protein-coding region. Although selection was apparently strong, high rates of recombination and a prolonged domestication period probably limited its effects. Our results help to explain why maize is such a variable crop. They also suggest that maize domestication required hundreds of years, and confirm previous evidence that maize was domesticated from Balsas teosinte of southwestern Mexico.

Molecular Diversity, Structure and Domestication of Grasses

“…estication events involving millions of plants. For instance, the patterns of diversity at the maize domestication gene tb1 are consistent with reasonably large effective population sizes being maintained during domestication (Wang et al, 1999).…”

“…Interestingly, this drop in diversity does not extend for the entire length of the gene, as the coding region has levels of diversity similar to those at neutral loci. Analysis of this data assuming a reasonable set of population genetic parameters suggests that the process of domestication could have taken at least hundreds of years for tb1 with only modest levels of selection (Wang et al, 1999). Other surveys in maize kernel starch accumulation have found additional genes involved in domestication and breeding (Buckler in preparation).…”

“…One maize gene involved in domestication, teosinte branched1, controls tillering and apical dominance, and was key in converting maize from a plant with multiple stalks (tillers) to a plant with a single tiller . The promoter of this locus has 61-fold lower diversity in the crop than it does in the closest wild relative (Wang et al, 1999). Interestingly, this drop in diversity does not extend for the entire length of the gene, as the coding region has levels of diversity similar to those at neutral loci.…”

Artificial selection of the melanocortin receptor 1 gene in Chinese domestic pigs during domestication

“…Our findings are consistent, however, with the logical theory of domestication events in that genetic diversity is generally thought to become lower after domestication. Lower genetic diversity could be caused by population dynamics or artificial selection, which evidently happens in several crops (for example, sorghum, rice and maize) (Wang et al, 1999;Hamblin et al, 2006;Olsen et al, 2006). By contrast, previous studies reported unexpectedly high sequence variation in domesticated pigs even when considering the influences of target genes on economically important traits and the presence of strong artificial selection (Ojeda et al, 2006(Ojeda et al, , 2008a.…”

A high-quality carrot genome assembly provides new insights into carotenoid accumulation and asterid genome evolution

“…4g,h) accumulation, including the selective sweep for y1 in maize, which extends 200 kb upstream and 600 kb downstream of the gene 47 . Rather, this scenario resembles the short sweep (60-90 kb) identified in maize around teosinte branched1 (tb1), a major domestication-associated gene 48 . A short sweep may reflect the highly effective rates of recombination expected in an outcrossing species like carrot.…”