Abstract
AbstractPremise of research. Change in base number of chromosomes per nucleus is usually believed to result from whole-genome duplication or from duplication or elimination of a single chromosome (aneuploidy). However, chromosome numbers can also change via mechanisms with no gain or loss of nuclear DNA, such as fusion or fission of chromosomes.Methodology. We previously determined amount of DNA per nucleus (2C values) using flow cytometry of leaf tissue. We tested whether Cycadales (cycad) chromosome numbers are correlated with these 2C values using ordinary least squares (OLS) and phylogenetic generalized least squares (PGLS) regression.Pivotal results. Regardless of branch length estimation technique and evolutionary model, OLS and PGLS yielded no statistically significant relationship between chromosome number and genome size in our analysis of 22 species, encompassing all 11 extant cycad genera.Conclusions. Within cycad genera, chromosomal fissions or fusions are much more likely than large additions...
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