title: Ultra Large Gene Families: A Matter of Adaptation or Genomic Parasites?
abstract: Gene duplication is an important mechanism of molecular evolution. It offers a fast track to modification, diversification, redundancy or rescue of gene function. However, duplication may also be neutral or (slightly) deleterious, and often ends in pseudo-geneisation. Here, we investigate the phylogenetic distribution of ultra large gene families on long and short evolutionary time scales. In particular, we focus on a family of NACHT-domain and leucine-rich-repeat-containing (NLR)-genes, which we previously found in large numbers to occupy one chromosome arm of the zebrafish genome. We were interested to see whether such a tight clustering is characteristic for ultra large gene families. Our data reconfirm that most gene family inflations are lineage-specific, but we can only identify very few gene clusters. Based on our observations we hypothesise that, beyond a certain size threshold, ultra large gene families continue to proliferate in a mechanism we term "run-away evolution". This process might ultimately lead to the failure of genomic integrity and drive species to extinction.
authors: Institute for Genetics, University of Cologne, Köln 50674, Germany. philipp.schiffer@gmail.com.|Division of Biosciences, GEE, University College London, London WC1E 6BT, UK. philipp.schiffer@gmail.com.
authors: Philipp H
authors: PH
authors: Schiffer
authors: Institute for Genetics, University of Cologne, Köln 50674, Germany. jgraveme@smail.uni-koeln.de.
authors: Jan
authors: J
authors: Gravemeyer
authors: Institute for Genetics, University of Cologne, Köln 50674, Germany. martina.rauscher@uni-koeln.de.
authors: Martina
authors: M
authors: Rauscher
authors: Institute for Genetics, University of Cologne, Köln 50674, Germany. twiehe@uni-koeln.de.
authors: Thomas
authors: T
authors: Wiehe
keywords: NLR-genes; adaptation; gene clusters; gene family; genome evolution; neutral evolution; run-away-evolution; selection