Corresponding author: Lorenzo Peruzzi (

Academic editor: M. Guerra

Until now, basic karyological parameters have been used in different ways by researchers to infer karyological relationships among organisms. In the present study, we propose a standardized approach to this aim, integrating six different, not redundant, parameters in a multivariate PCoA analysis. These parameters are chromosome number, basic chromosome number, total haploid chromosome length, M_{CA} (Mean Centromeric Asymmetry), CV_{CL} (Coefficient of Variation of Chromosome Length) and CV_{CI} (Coefficient of Variation of Centromeric Index). The method is exemplified with the application to several plant taxa, and its significance and limits are discussed in the light of current phylogenetic knowledge of these groups.

Peruzzi L, Altınordu F (2014) A proposal for a multivariate quantitative approach to infer karyological relationships among taxa. Comparative Cytogenetics 8(4): 337–349. doi:

Chromosomes, especially those of plants, have been efficient material for almost every kind of cytogenetic research (

The karyotype of a species is generally subject to little variation and it is generally assumed that two similar species can be different for a number of chromosome rearrangements correlated with phylogenetic distance among them (

Hence, the aims of our study were (1) to propose a standardized use of basic karyological characters as a valid, of general use, complement to other source of systematic data to understand the relationships among taxonomic groups as families, tribes, genera, sections and species, and (2) to demonstrate the using of this new quantitative method in cytotaxonomy in selected groups, for which data were available in literature.

The data about

To determine the karyological relationships among taxa, we used chromosome number (2_{CA} (Mean Centromeric Asymmetry) which gives a measure of intrachromosomal asymmetry, and CV_{CL} (Coefficient of Variation of Chromosome Length) which gives a measure of interchromosomal asymmetry, together with CV_{CI} (Coefficient of Variation of Centromeric Index), which gives a measure of centromere position heterogeneity (_{CA} is calculated as the mean (L-S)/(L+S) ×100 where, for each chromosome, L is the length of long arm and S is the length of short arm; CV_{CL} as the standard deviation of (L+S) divided by the mean (L+S) ×100; CV_{CI} as the standard deviation of S/(L+S) divided by the mean S/(L+S) ×100. These three parameters estimate quantitatively three different features of a karyotype, so that any redundancy of data is avoided. Moreover, they were shown to be the only quantitative parameters correct on statistical grounds (_{1}, CG; for details and references see

Other karyological characters might have been used, such as number of 45S and 5S sites or “best practice” genome size estimations, but this kind of data is not yet widespread (

Since our main objective was to highlight correctly karyological relationships among objects (e.g. single accessions) and not to form groups, we avoided multivariate classification techniques such as cluster analysis etc. and focused on a general ordination method as PCoA (Principal Coordinate Analysis). In cases where specific

We analyzed 434 accessions for _{CI}, and M_{CA}.

PCoA for

Within _{CL}, and M_{CA}.

PCoA for

Within _{CA}, and CV_{CL}.

PCoA for Tulipeae genera based on 6 quantitative karyological parameters (Axis 1 vs. Axis 2). The two

We analyzed 24 accessions belonging to three sections (_{CI}, and THL.

PCoA for

PCoA for

We analyzed 36 accessions belonging to nine species of _{CL}, and M_{CA}.

PCoA for

Our method allows to describe basic karyological relationships among taxa in a correct way, avoiding redundant data or the use of statistically not well founded parameters. Concerning the examples presented, there is always a certain degree of agreement among the information resulting from karyological multivariate analysis and the available phylogenetic information (used to form the groups highlighted in the PCoA and tested by means of DA).

For various reasons, researchers used until very recently outdated, wrong or redundant parameters in order to establish relationships among taxa. We propose here a standardized method, taking into account six quantitative parameters: 2_{CI} (Coefficient of Variation of Centromeric Index, measuring the heterogeneity in the centromere position), M_{CA} and CV_{CL} (Mean Centromeric Asymmetry and Coefficient of Variation of Chromosome Length, both measuring the karyotype asymmetry). We used a multivariate ordination approach (PCoA), eventually complemented by DA, if specific grouping hypotheses need to be tested. We think this method is best suited to establish karyological relationships, relationships, compared with classification approaches (i.e. clustering, used for instance by

Karyological parameters available for the studied taxa

measurement

Excel file with three different worksheets (