CHIASMA LOCALIZATION, HETEROCHROMATIN AND SYNAPTONEMAL COMPLEXES IN THE GRASSHOPPER PYRGOMORPHA-CONICA

Surface-spread synaptonemal complexes and chiasma distributions in spe rmatocytes with different C-banding patterns and chiasma distributions in oocytes were analyzed in the grasshopper Pyrgomorpha conica. Male meiosis was characterized by a proximal/distal chiasma localization an d complete pairing of homologous chromosomes at pachytene. However, th ere were indications of a relationship between the frequency and locat ion of pairing initiation sites and chiasma distribution. The presence of a proximal supernumerary segment in a medium-sized chromosome does not increase the mean cell chiasma frequency of carrier individuals c ompared with those lacking it but may modify chiasma distribution in a t least some carrier bivalents. This effect could be related to hetero synapsis in the region near the segment. Mean cell chiasma frequency w as significantly lower in females than in males. Females also showed a ltered chiasma distributions compared with males, with fewer proximal chiasmata and more interstitial and distal chiasmata.