RECOMBINATION PARAMETERS IN SOME 23-CHROM OSOME SPECIES OF GRASSHOPPERS

The frequency and distribution of recombinational interchanges along t he bivalent length in male meiosis were investigated by cytological me thods in five species of grasshoppers with 23 acrocentric chromosomes and of different taxonomic groups. In two species, the mode of synapto nemal complex (SNC) formation was analyzed. This allowed to differenti ation of two types of interchange distribution and SNC formation mode in large and medium chromosomes: (1) Chiasmata are formed predominantl y in distal and proximal chromosome regions. SNC formation also starts from both ends of a bivalent. (2) The interchange frequency increases only in the distal chromosome region. Pairing of lateral SNC elements begins from the distal region. The influence of the mode of SNC forma tion on the type of interchange distribution is discussed. The similar ity of these parameters in related species, as well as their differenc es in species having an equal chromosome number but belonging to diffe rent tribes, is emphasized.