Campanella, Donald M. .
Genetic equilibrium of Taraxacum-type apomixis in autonomous triploid lineages.
Meiotic diplospory is an unusual mechanism of gametophytic apomixis that occurs in dandelions (Taraxacum spp.) and a few other angiosperm taxa. Crossing-over during prophase I of meiotic diplospory has the potential to contribute genotypic diversity to apomictic lineages, and C. D. Darlington described this process as “subsexual reproduction" because it involves homologous recombination without fertilization. I developed stage-structured matrix models of meiotic diplospory to examine factors influencing genetic equilibrium within apomictic lineages. Stable stage structures of triploid genotypes were determined across a broad range of probabilities for crossing-over and mutation, using either two or three alleles of a single locus, and assuming the absence of fertilization or ecological factors such as selection pressure. The models serve to illustrate how crossing-over promotes homozygosity in meiotic diplosporous lineages, while mutation initiates heterozygosity. The full spectrum of homozygous and heterozygous combinations was found to be stable at equilibrium in triploid lineages when crossing-over and mutation probabilities are approximately equal, but stable distributions are highly skewed by differences in those transitions. The analysis supports predictions of genotypic diversity in apomictic dandelions, but it also indicates that population genetic structure could be very sensitive to variation in transition rates. Meiotic diplospory may have the effect of generating polymorphisms under gradual rates of crossing-over, but higher rates of crossing-over also could facilitate the unloading of deleterious alleles. Improved empirical estimates of the relative rates of crossing-over and mutation are needed to evaluate the importance of meiotic diplospory in dandelion populations, and models could incorporate more realistic genetic conditions such as facultative cross-fertilization, aneuploidy, or greater numbers of alleles.
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1 - Oregon State University, Dept. of Botany & Plant Pathology, 2082 Cordley Hall, Corvallis, Oregon, 97331-2902, USA
Presentation Type: Poster:Posters for Topics
Location: Ball Room & Party Room/SUB
Date: Monday, July 28th, 2008
Time: 12:30 PM