CYTOGENETIC REGULARITIES IN SYNAPSIS OF M EIOTIC CHROMOSOMES IN ANIMALS AND PLANTS

Chromosome synapsis in meiosis is performed through the formation of a synaptonemal complex (SC). The SC aggregates homologues until the dip lotene stage, when the function of physical binding is carried out by a chiasmata. SC formation is controlled by specific genes. Regularitie s of SC formation in animals and plants are being studied at the Labor atory of Cytogenetics, Vavilov Institute of General Genetics, the Russ ian Academy of Sciences. It was shown that, in Drosophila melanogaster , the presence or absence of SC in meiosis is determined by balance be tween autosomes and sex chromosomes, i.e., SC is formed according to r egularities in sex determination. The dose of the 8C-11A segment of X chromosome plays a key role in this process. Eight mutations in synapt ic genes that affect SC formation were studied in rye Secale cereale. SC variants occurring in heteromorphic sex chromosomes were analyzed i n the Ellobius genera and in B-chromosomes of Apodemus peninsulae. It was shown that, in addition to homologous synapsis, non-homologous syn apsis of aberrant chromosomes occurs in rye and mouse heterozygotes at chromosome rearrangements. Twice as many heterozygous chromosome rear rangements were revealed, when the SC was studied at pachytene instead of diakinesis and metaphase I. Simple methods of SC investigations ex tended the capabilities of cytogenetic analysis of meiosis and provide d new perspectives for studying the action of meiotic gen.