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The pattern and distribution of deleterious mutations in maize
Most non-synonymous mutations are thought to be deleterious because of their
effect on protein sequence. These polymorphisms are expected to be removed or
kept at low frequency by the action of natural selection, and rare deleterious
variants have been implicated as a possible explanation for the "missing
heritability" seen in many studies of complex traits. Nonetheless, the effect
of positive selection on linked sites or drift in small or inbred populations
may also impact the evolution of deleterious alleles. Here, we made use of
genome-wide genotyping data to characterize deleterious variants in a large
panel of maize inbred lines. We show that, in spite of small effective
population sizes and inbreeding, most putatively deleterious SNPs are indeed at
low frequencies within individual genetic groups. We find that genes showing
associations with a number of complex traits are enriched for deleterious
variants. Together these data are consistent with the dominance model of
heterosis, in which complementation of numerous low frequency, weak deleterious
variants contribute to hybrid vigor
Genetic, evolutionary and plant breeding insights from the domestication of maize.
The natural history of maize began nine thousand years ago when Mexican farmers started to collect the seeds of the wild grass, teosinte. Invaluable as a food source, maize permeated Mexican culture and religion. Its domestication eventually led to its adoption as a model organism, aided in large part by its large chromosomes, ease of pollination and growing agricultural importance. Genome comparisons between varieties of maize, teosinte and other grasses are beginning to identify the genes responsible for the domestication of modern maize and are also providing ideas for the breeding of more hardy varieties
Hydrodynamic Irreversibility in Particle Suspensions with Non-Uniform Strain
A dynamical phase transition from reversible to irreversible behavior occurs
when particle suspensions are subjected to uniform oscillatory shear, even in
the Stokes flow limit. We consider a more general situation with non-uniform
strain (e.g. oscillatory channel flow), which is observed to exhibit markedly
different dynamics. Self-organization and shear-induced migration only
partially explain the delayed, simultaneous onset of irreversibility across the
channel. The onset of irreversibility is accompanied by long-range correlated
particle motion. This motion leads to particle activity even at the channel
center, where the strain is negligible, and prevents the system from evolving
into a reversible state
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