Genetics. Published Articles Ahead of Print: April 28, 2006, Copyright © 2006
doi:10.1534/genetics.106.055624


A more recent version of this article appeared on July 1, 2006.


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Genetic map-based analysis of genome structure in the homosporous fern Ceratopteris richardii

1 Indiana University

* To whom correspondence should be addressed. E-mail: tnakazat{at}indiana.edu.

Submitted on January 11, 2006
Revised on March 15, 2006
Accepted on 18 April 2006


Abstract

Homosporous ferns have extremely high chromosome numbers relative to flowering plants , but the species with the lowest chromosome numbers show gene expression patterns typical of diploid organisms, suggesting that they maybe diplodized ancient polyploids. To investigate the role of polyploidy in fern genome evolution, and to provide permanent genetic resources for this neglected group, we constructed a high-resolution genetic linkage map of the homosporous fern model species, Ceratopteris richardii (n = 39). Linkage map construction employed 488 Doubled Haploid Lines (DHLs) that were genotyped for 368 RFLP, 358 AFLP, and 3 isozyme markers. Forty-one linkage groups were recovered, with average spacing between markers of 3.18 cM. Most loci (~76%) are duplicated and most duplicates occur on different linkage groups, indicating that as in other eukaryotic genomes, gene duplication plays a prominent role in shaping the architecture of fern genomes. Although past polyploidization is a potential mechanism for the observed abundance of gene duplicates, a wide range in the number of gene duplicates as well as the absence of large syntenic regions consisting of duplicated gene copies imply that small-scale duplications may be the primary mode of gene duplication in C. richardii. Alternatively, evidence of past polyploidization(s) may be masked by extensive chromosomal rearrangements as well as smaller-scale duplications and deletions following polyploidization(s).

Key Words: Ceratopteris richardii, homosporous fern, linkage map, paleopolyploidy




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T. Nakazato, M.-K. Jung, E. A. Housworth, L. H. Rieseberg, and G. J. Gastony
A Genomewide Study of Reproductive Barriers Between Allopatric Populations of a Homosporous Fern, Ceratopteris richardii
Genetics, October 1, 2007; 177(2): 1141 - 1150.
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