title: Guided genome halving: hardness, heuristics and the history of the Hemiascomycetes.
abstract: BACKGROUND
  Some present day species have incurred a whole genome doubling event in their evolutionary history, and this is reflected today in patterns of duplicated segments scattered throughout their chromosomes. These duplications may be used as data to 'halve' the genome, i.e. to reconstruct the ancestral genome at the moment of doubling, but the solution is often highly nonunique. To resolve this problem, we take account of outgroups, external reference genomes, to guide and narrow down the search.
  
  
  RESULTS
  We improve on a previous, computationally costly, 'brute force' method by adapting the genome halving algorithm of El-Mabrouk and Sankoff so that it rapidly and accurately constructs an ancestor close the outgroups, prior to a local optimization heuristic. We apply this to reconstruct the predoubling ancestor of Saccharomyces cerevisiae and Candida glabrata, guided by the genomes of three other yeasts that diverged before the genome doubling event. We analyze the results in terms (1) of the minimum evolution criterion, (2) how close the genome halving result is to the final (local) minimum and (3) how close the final result is to an ancestor manually constructed by an expert with access to additional information. We also visualize the set of reconstructed ancestors using classic multidimensional scaling to see what aspects of the two doubled and three unduplicated genomes influence the differences among the reconstructions.
  
  
  BACKGROUND
  The experimental software is available on request.
authors.affiliation: Department of Biology, University of Ottawa, Ottawa, Ontario, Canada.
authors.forename: Chunfang
authors.initials: C
authors.lastname: Zheng
authors.forename: Qian
authors.initials: Q
authors.lastname: Zhu
authors.forename: Zaky
authors.initials: Z
authors.lastname: Adam
authors.forename: David
authors.initials: D
authors.lastname: Sankoff
mesh_terms: D000465:Algorithms; D001203:Ascomycota / Q000235:genetics*; D001483:Base Sequence; D002874:Chromosome Mapping / Q000379:methods*; D020440:Gene Duplication; D016681:Genome, Fungal / Q000235:genetics*; D008969:Molecular Sequence Data; D017422:Sequence Analysis, DNA / Q000379:methods*