Karyotype asymmetry: again, how to measure and what to measure?

Abstract

One of the most popular, cheap and widely used approaches in comparative cytogenetics – especially by botanists – is that concerning intrachromosomal and interchromosomal karyotype asymmetry. Currently, there is no clear indication of which method, among the many different ones reported in literature, is the most adequate to infer karyotype asymmetry (especially intrachromosomal), above all in view of the criticisms recently moved to the most recent proposal published. This work addresses a critical review of the methods so far proposed for estimation of karyotype asymmetry, using both artificial and real chromosome datasets. It is shown once again how the concept karyotype of asymmetry is composed by two kinds of estimation: interchromosomal and intrachromosomal asymmetries. For the first one, the use of Coefficient of Variation of Chromosome Length, a powerful statistical parameter, is here confirmed. For the second one, the most appropriate parameter is the new Mean Centromeric Asymmetry, where Centromeric Asymmetry for each chromosome in a complement is easily obtained by calculating the difference of relative lengths of long arm and short arm. The Coefficient of Variation of Centromeric Index, strongly criticized in recent literature, is an additional karyological parameter, not properly connected with karyotype asymmetry. This shows definitively what and how to measure to correctly infer karyotype asymmetry, by proposing to couple two already known parameters in a new way. Hopefully, it will be the basic future reference for all those scientists dealing with cytotaxonomy.

Cytogenetic analyses as clarifying tools for taxonomy of the genus Callisia Loefl. (Commelinaceae)

“…Karyotype asymmetry was estimated using the Mean Centromeric Asymmetry (MCA) and Coefficien of Variation (CVCL) of Peruzzi & Eroğlu (2013), as well as the categories of Stebbins (1971).…”

A karyomorphological study on the genus Muscari Mill. growing in Kahramanmaraş (Turkey)

“…Preparations were examined using an Olympus BX53 light microscope equipped with a digital camera. Moreover, measurements of somatic chromosomes were taken by CAMERAM software; they were calculated with a formula of the relative variation in chromosome length (CV CL ) and mean centromeric asymmetry (M CA ) (Zuo and Yuan, 2011;Peruzzi and Eroğlu, 2013). The classification of chromosomes as having metacentric (m), submetacentric (sm), subtelocentric (st), and telocentric (t) centromeres was used, according to Levan et al (1964).…”

Genetic Relationship between Vasconcellea and Carica Based on Their Chromosome Features

“…According to Huziwara (1962) the TF% index can range from zero to 50% and karyotypes with index value closer to 50% are considered extremely symmetrical and the one closer to zero is asymmetrical. The Syi index might vary from 0, asymmetric, when the mean short arm length is equal to zero (S=0), to 1 or 100%, when the median short arm length is equal to median of long arm length (S=L) a symmetry karyotype (Greilhuber and Speta 1976, Verona et al 2002, Peruzzi and Eroglu 2013. Our results suggest that all species have symmetrical karyotypes.…”