478 ISSN 0095-4527, Cytology and Genetics, 2018, Vol. 52, No. 6, pp. 478–483. © Allerton Press, Inc., 2018. Enigmatic Phenomenon of Secondary Association among Bivalents in Guar (Cyamopsis tetragonoloba (L.) Taub.) 1 G. Kumar a and S. Singh a, * a Plant Genetics Laboratory, Department of Botany, University of Allahabad, Allahabad, Uttar Pradesh, India *e-mail: shefalisingh.910@gmail.com Received June 1, 2017 Abstract—Cytogenetical assessment of pollen mother cells of Guar (Cyamopsis tetragonoloba (L.) Taub.) in response to treatment of chemical mutagen was done. Ethyl Methane Sulphonate (EMS) revealed possession of an enigmatic behaviour among chromosomal bivalents i.e. formation of secondary association. Chromo- somes exhibited a unique tendency of getting associated in close proximity and form discrete pairs. The phe- nomenon of secondary chromosomal association has been ascribed to the existence of similar cohesive homology or malfunctioning in chiasma formation among the associating bivalents. The association of biva- lents was witnessed to be executed in either end to end fashion or sideways association. Various other chro- mosomal abnormalities were found, but secondary association was the preponderant abnormality which exhibited a continuous increase in its magnitude with increase in EMS concentration. Along with secondary associations, stickiness of chromosomes at anaphase was observed in considerable frequency. A significant influence of chromosomal association on the post meiotic product was also experienced, which in turn, led to influence the meiotic index. Abnormal sporads in the form of triads, dyads, monads and polyads, along- with normal tetrad were seen. Pollen fertility percent was seen to decline from control to the highest concen- tration of EMS due to anomalies of preceding stages. Keywords: Guar, pollen mother cells (pmc), secondary association, Meiotic Index (MI), pollen fertility DOI: 10.3103/S0095452718060075 INTRODUCTION Studies planned for examining meiosis may prove informatory in decoding concealed mysteries regard- ing the mode and mechanism of inheritance. Estab- lishment of meiotic cycles has been provisioned in nature to create numerical homogeneousity among organisms of a species in terms of chromosome num- ber and ploidy. Stable genetic traits are governed by the inheritance of normal functioning chromosomal com- plement. However irregularity or novelty among traits is the outcome of alteration in the genetic compo- nents. The irregularities are needed to be rectified for continuity of life whereas novelties may standout as forbearer for the establishment of new genetic trait. Henceforth, there is a necessity to study the behavioral properties of chromosomes to unveil the forbidden features which would perhaps assist in deciphering clues of inheritance. Plants with differential basic number occur in sev- eral plant species. Cytogenetical investigation for this numerical asymmetry and differential basic number led to the initial inclination to the concept so called as “secondary association”. The association of more than two chromosomes at metaphase of meiosis was first demonstrated by Kuwada [1] in Oryza sativa in polyploids. Later researchers like Ishikawa [2] in Dahlia variabilis and Marchal [3] in Amblystegium have also reported about its occurrence. The term “secondary association” was, however, first suggested by Darlington and Moffet [4]. However a conclusively precise explanation to this enigmatic phenomenon was provided by Darlington [5], where he described secondary association as “presence of bivalents/chro- mosomes in pairs or groups in close proximity having diffused connections”. Jelenkovic [6] stated that secondary associations may be due to the presence of heterochromatin region in the genome which facilitates the association between non-homologous parts. Lawrence [7] explained this phenomenon on the basis of homology and said that a homology existed between the paired bivalents, which results in a side by side association of bivalents in groups; this view was also supported [8]. Sometimes mutagenic action also leads to incite con- spicuous secondary chromosomal pairing as reported in Phaseolus vulgaris in response to combined mutagen treatment of Gamma rays and Sodium azide [9]. The present study was planned to screen out the effect of mutagens EMS on the pollen mother cells of Cyamopsis tetragonoloba (L). Taub. (also known as 1 The article is published in the original.