Excess Heterozygosity Contributes to Genetic Map Expansion in Pea Recombinant Inbred Populations

Corresponding author: M. R. Knox, John Innes Centre, Norwich Research Park, Colney Ln., Norwich NR4 7UH, UK., maggie.knox{at}bbsrc.ac.uk (E-mail)

Communicating editor: J. A. BIRCHLER

Several plant genetic maps presented in the literature are longer than expected from cytogenetic data. Here we compare F₂ and RI maps derived from a cross between the same two parental lines and show that excess heterozygosity contributes to map inflation. These maps have been constructed using a common set of dominant markers. Although not generally regarded as informative for F₂ mapping, these allowed rapid map construction, and the resulting data analysis has provided information not otherwise obvious when examining a population from only one generation. Segregation distortion, a common feature of most populations and marker systems, found in the F₂ but not the RI, has identified excess heterozygosity. A few markers with a deficiency of heterozygotes were found to map to linkage group V (chromosome 3), which is known to form rod bivalents in this cross. Although the final map length was longer for the F₂ population, the mapped order of markers was generally the same in the F₂ and RI maps. The data presented in this analysis reconcile much of the inconsistency between map length estimates from chiasma counts and genetic data.

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