A SUPERNUMERARY CHROMOSOME SEGMENT IN LOCUSTA-MIGRATORIA

A single female of Locusta migratoria was found to be heterozygous for a supernumerary heterochromatic segment distally located on the M6 au tosome close to its nucleolus organiser region (NOR). Reactions to sev eral chromosome banding techniques revealed its heterochromatic nature and its composition of GC-rich DNA sequences and likewise the NORs in this species. This suggests an origin for the extra segment by amplif ication of GC-rich DNA sequences contained in the distal NOR of the M6 Chromosome, which is reinforced by the observation that the NOR of se gmented M6 chromosomes produced the larger nucleolus in embryo prophas e cells, such as would be expected from the presence of rRNA genes in the extra segment. No accumulation mechanism was detected in this fema le after analyzing the 213 embryo offspring produced, but an increase in the number of nucleoli per interphase nucleus was noted in heterozy gous embryos in respect to standard homozygous ones.