Crossing design shapes patterns of genetic variation in synthetic recombinant populations of Saccharomyces cerevisiae

“Synthetic recombinant” populations have emerged as a useful tool for
dissecting the genetics of complex traits.  They can be used to
derive inbred lines for fine QTL mapping, or the populations themselves
can be sampled for experimental evolution.  In latter
application, investigators generally value maximizing genetic variation in
constructed populations. This is because in evolution experiments
initiated from such populations, adaptation is primarily fueled by
standing genetic variation. Despite this reality, little has been done to
systematically evaluate how different methods of constructing synthetic
populations shape initial patterns of variation. Here we seek to address
this issue by comparing outcomes in synthetic recombinant Saccharomyces
cerevisiae populations created using one of two strategies: pairwise
crossing of isogenic strains or simple mixing of strains in equal
proportion.  We also explore the impact of the varying the number
of parental strains. We find that more genetic variation is initially
present and maintained when population construction includes a round of
pairwise crossing.  As perhaps expected, we also observe that
increasing the number of parental strains typically increases genetic
diversity. In summary, we suggest that when constructing populations for
use in evolution experiments, simply mixing founder strains in equal
proportion may limit the adaptive potential.