In the Light of Evolution Volume III: Two Centuries of Darwin (2009) / Chapter Skim
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6 Tracking Footprints of Maize Domestication and Evidence for a Massive Selective Sweep on Chromosome 10--Feng Tian, Natalie M. Stevens, and Edward S. Buckler IV
6 Tracking Footprints of Maize Domestication and Evidence for a Massive Selective Sweep on Chromosome 10--Feng Tian, Natalie M. Stevens, and Edward S. Buckler IV
Pages 111-128
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From page 111... ...
BUCKler iv†‡ Maize domestication is one of the greatest feats of artificial selec tion and evolution, wherein a weedy plant in Central Mexico was converted through human-mediated selection into the most pro ductive crop in the world. In fact, the changes were so astounding that it took much of the last century to identify modern maize's true ancestor.
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From page 112... ...
one key question concerning maize domestication remains to be resolved: Was maize domestication the result of selection on a small number of loci with large effects, a large number of loci with small effects, or both? recent genetic evidence has provided clues about the relative contributions of large-effect and small-effect loci.
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From page 113... ...
. essentially, every new teosinte in its own genetic technology and approach developed over the last century has been 15pc applied in an effort to resolve the question of precisely how teosinte and modern maize are related genetically.
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From page 114... ...
Despite these profound physical differences and controversial hypotheses, various morphological, cytological, and genetic studies would eventually delineate relationships within the genus Zea.
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From page 115... ...
in general, population genetic theory predicts that the level of selectively neutral molecular diversity is a joint function of mutation rate and effective population size, both of which would seem to be large in Z mays ssp.
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From page 116... ...
recent quantitative trait loci (QTl) analyses have provided evidence supporting the notion that a few regions of the maize genome specify the key traits that distinguish maize from teosinte.
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From page 117... ...
. Because this locus represents a key step in maize domestication, its nucleotide diversity should be reduced when compared with neutral sites.
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From page 118... ...
if the maize genome contains 59,000 genes, Wright et al.'s estima tion suggested that a minimum of 1,200 genes throughout the genome have been targets of selection during maize domestication. starch is the key product of maize, accounting for 73% of the kernel's total weight.
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From page 119... ...
To investigate the signature of selection in this region in more detail, we sequenced 22 loci spanning ≈4 Mb in a panel of 28 diverse maize inbreds and 16 teosinte (Z. mays ssp.
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From page 120... ...
for maize and teosinte along the investigated regions on chromosome 10. The dotted line and dashed line represent the average nucleotide diversity of 774 genes (Wright et al., 2005)
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From page 121... ...
. N, number of sequence; l, the length of a given locus; s, number of segregating sites; π and θ were estimated for noncoding and synonymous sites; k, divergence between maize or teosinte and Tripsacum dactyloides.
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From page 122... ...
(iii) We evaluated the probability of the observed reduction of genetic diversity in maize relative to teosinte under the neutral maize domestication bottleneck model.
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From page 123... ...
. however, because the Clr test is under the assumption of a randomly mating population of constant size, undetected population structure or a recent bottleneck might produce a similar nucleotide variation pattern as selective sweep (Jensen et al., 2005)
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From page 124... ...
For understanding selection, the patterns are tremendously varied. We have examples of nearly every type of selection footprint: on standing variation and on novel mutations, a few large-effect genes and large numbers of selected genes with apparently small phenotypic effects, small single selective sweeps, and a few massive sweeps.
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From page 125... ...
MATERIALS AND METHODS Plant Materials and DNA Sequencing We sampled DnA sequence diversity in a panel of 28 diverse maize inbreds and 16 teosinte (Z. mays ssp.
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From page 126... ...
was used as an outgroup to estimate divergence. A total of 23 loci were surveyed to identify the physical boundary of the selective sweep region based on the maize FPC map (www.genome.arizona.edu/fpc/maize)
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From page 127... ...
was further used to distinguish between selective sweep and demographic forces. The significance of the GoF value for the observed data was evaluated by 1,000 simulations under the selection scenario produced by the above Clr test.
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