Secondary Association in the Castor Oil Plant

Abstract

A study of pollen mother cells of the castor oil plant (Ricinus communis L.; 2n=20) at diakinesis and metaphase I (MI) of meiosis reveals associations of more than two chromosomes.These consist of groups of presumably non-homologous bivalents associated in various degrees of intimacy. Thus one may observe loose side by side associations of pairs as well as apparent configurations of four chromosomes reminiscent of quadrivalents or translo cations; (figs. 11-15). Richharia (1937) and Kurita (1946) have reported secondary association in Ricinus at metaphase I and later stages of meiosis. The general phe nomenon of secondary association was first observed by Kuwada (1910) in Oryza sativa. Darlington (1928) and Lawrence (1931) were the first to re late this phenomenon of side by side association of bivalents in groups of two, three or more, to the homology existing between these bivalents. Primary pairing at zygotene and chiasma formation between more than two homolog ous chromosomes were known to result in multivalents. This type of pairing was considered as distinct from secondary pairing (or association) in which there is only a loose association of bivalents without chiasmata connecting them. According to these authors this association between pairs starts only at prometaphase and metaphase I and continues into the later meiotic stages. They suggested that chromosomes which have secondary association are homolog ous or partially so, and reflect the polyploid origin of the species exhibiting this phenomenon.More recently Brown (1950) has shown that in Luzula, secondary as sociation at metaphase I is an artifact of the squash technique. Stebbins (1950) recognizes that secondary association serves in many cases as an in dication of the polyploid origin of a species or genus, but he cautions against elaborate phylogenetic conclusions based on such evidence.Chromosome homology has been presumed to be the basic element com mon to both primary and secondary association (Lawrence 1931). However, only recently attempts have been made (Linnert 1949, Peters 1954, Gottschalk 1955 to look for interchromosomal relationships in prophase stages of meiosis, which might correspond to secondary association.

Fusion of centromeres and star formatons at pachytene of Cajanus × Atylosia hybrids

“…This is analogous to what has been found in Cajanus xAtylosia hybrids. Jakob (1957) reported H-and cross-shaped configurations of four chromosomes (two bivalents) at pachytene of Ricinus, which are analogous to the present star formation. He found a correspondence between these interchromosomal associations at pachytene and the secondary associations at diakinesis.…”

Secondary association of bivalents in Cissus discolor Blume.

“…Secondary association has been considered as an evidence of remote affinity between the chromosomes (Darlington 1928, Lawrence 1931and Riley 1960) and shown to be of wide spread occurrence in polyploids (Jakob 1957) . Brown (1950) and Heilborn (1936) consider it as an artefact.…”

Pollen Mother Cell Analysis of Intraspecies Hybrid of <i>Gossypium arboreum</i> Linn., Indicating Secondarily Balanced Polyploidy

“…During the pachytene analysis of Ricinus communis Jakob (1957) noticed secondary association in early diakinesis, he postulated that primary and secondary pairings could be attributed to the same origin.…”