PSEUDO-MULTIPLE FORMATION AS A CONSEQUENCE OF PROLONGED NON-HOMOLOGOUS CHROMOSOME ASSOCIATION IN METRIOPTERA BRACHYPTERA

Multiple configurations involving the L3 and L4 homologues have been observed in all individuals from a population sample of Metrioptera brachyptera. These associations which persist up to and including metaphase of the first meiotic division are non-homologous and achiasmate in character. They are conditioned by the persistent association of large distally located heterochromatic blocks on the L3 and L4 chromosomes and are not, as White has proposed, the result of crossing over in translocated terminal duplications. When the L3 and L4 chromosomes form bivalents the distal heterochromatin restricts crossing over in this region and chiasmata are localised proximally. In other members of the complement chiasmata are localised at either or both the centric and telomeric ends. A relationship is demonstrated between the pattern of chiasma localization and that of chromosome pairing.