2004 The Society for the Study of Evolution. All rights reserved.
Evolution, 58(4), 2004, pp. 702709
INTRATETRAD MATING AND THE EVOLUTION OF LINKAGE RELATIONSHIPS
JANIS ANTONOVICS1 AND JOSEPH Y. ABRAMS
Department of Biology, University of Virginia, Charlottesville, Virginia 22904
Abstract. Mating among the immediate products of meiosis (intratetrad mating) is a common feature of many or-
ganisms with parthenogenesis or with mating-type determination in the haploid phase. Using a three-locus deterministic
model we show that intratetrad mating, unlike other systems of mating, allows sheltering of deleterious recessive
alleles even if there is only partial linkage between a mating locus and a load locus. Moreover, modifiers that reduce
recombination between the load and mating-type locus will spread to fixation, even when there is no linkage dis-
equilibrium between these loci in the population as a whole. This seeming contradiction to classical expectation is
because partial linkage generates linkage disequilibrium among segregating loci within a tetrad, which then acts as
the ``mating unit.''
Key words. Automixis, centromere interference, genetic load, haplo-lethal, mating-type bias, Microbotryum, self-
Received September 5, 2002. Accepted December 30, 2003.
In many genomes, regions that are maintained in a per-
manently heterozygous state have been implicated in the shel-