TANDEM DUPLICATION OF NUCLEOLUS ORGANIZER REGION (NOR) IN THE JAPANESE MACAQUE, MACACA-FUSCATA-FUSCATA

During exploration of chromosome polymorphisms in Japanese macaques, a heteromorphic polymorphism was found in a population in the Zigokudan i monkey park. The population consisted of three troops (social units) . Of 36 monkeys examined, five females showed heterozygotic 'marker' c hromosome (chromosome 9). The polymorphism was a tandem duplication of the nucleolus organizer region (NOR) of the short arm of chromosome 9 , which was found for the first time in the genus Macaca. FISH and fib re-FISH using human 18S rDNA and sequential silver nitrate staining re vealed that the duplicated region included a part of the euchromatic s atellite and the stalk and that the euchromatic block (intercalary sat ellite) divided the NOR into two parts (distal and proximal). Furtherm ore, it showed that the distal region possessed much more rDNA than th e proximal region, and that the duplications might have been introduce d via a mechanism of gene amplification (inverted duplications associa ted with over-replication and recombination events). As the tandem dup lication was observed sporadically in four maternal pedigrees in two t roops and the mothers of the variants all had normal chromosomes, the variation might have been introduced from another population's gene po ol by a solitary male immigrant.