Up to date, little is known about polyploidy in system groups that have the gametophyte as the dominant phase. Although the sporophyte generation dominates in most extant lineages of land plants, in the earliest groups of land plants and also in several macroalgal groups, the gametophyte generation was (and it still is) the dominant component of the life cycle. This cycle alternates between sporophytes (spore-producing organisms) and gametophytes (gamete-producing organisms) 9. Brassica, Cotton, Maize, Spartina, Wheat, Tragopogon) representing life cycles in which the sporophyte is the dominant phase in a complex cycle. In polyploid research, most of the systems studied are higher plants (e.g. These findings have renewed the interest in examining WGD as an evolutionary process 6, 7, which coupled with molecular genetics and phylogenetic analyses can provide new insights into the evolution of the genome 8. Recent studies have also demonstrated that polyploid genomes can be highly dynamic and undergo rapid structural and functional changes. While whole genome duplication (WGD) is now accepted as an important evolutionary force, the genetic factors and the life history implications affecting the existence and abundance of polyploid lineages are still poorly understood 3, 4, 5. In angiosperms, many species have been suggested to have polyploid ancestry 2. In fact, most flowering plants and vertebrates descend from polyploid ancestors 1.
Polyploidy, the increase in genome size by the acquisition of more than one set of chromosomes has been a key factor in eukaryote evolution. New hypotheses for the life histories of Porphyra species are discussed. We conclude that the gametophytic phase ( n) in Porphyra species is not haploid, contradicting previous theories. linearis, genetic differentiation was found among three polyploid lineages: triploid, tetraploid and mixoploids, representing different evolutionary units. Multiple ploidy levels and genome sizes were found in Porphyra species, representing different cell lines and comprising several cytotype combinations among the same and different individuals. linearis) were used in comparisons of ploidy levels, genome sizes and genetic differentiation using flow cytometry and 11 microsatellite markers among putative polyploid lineages.
In this study, we address such questions in a novel system ( Porphyra, red algae) where the gametophyte is the dominant phase in the life history. Polyploidy has been mainly studied in plant model species in which the sporophyte is the dominant phase in their life history. Whole genome duplication is now accepted as an important evolutionary force, but the genetic factors and the life history implications affecting the existence and abundance of polyploid lineages within species are still poorly known.
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