BIOLOGICAL STUDIES ON ANCESTORAL INSECT SPECIES OF THE SILKWORM,BOMBYXMORI

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The gonads of males B.mandarina larvae from day 2 of the fourth instar to day 2 of the fifth instar were found to be at the premiotic stage and suitable for the counting of 2n chromosome number. On day 4 of the fifth instar the gonads were at the first meiotic prophase stage and used for the observation of haploid chromosome number. The B.mandarina individuals from Taegu City of Korea, Tsushima Island of Japan and Fukuoka City of Japan had 2n=54, n=27. On the other hand, individuals from China possessed 2n=56, n=28. No differences were observed in morphological features of the chromosomes among the specimens.PCR was designed to obtain the products covering the entire intron 3 and a part of exon 4 of the arylphorin gene and thus may be 409 bp in size according to the data for B.mori. Among several amplified bands obtained in the first PCR,a band of aporoximately 500 bp was extracted from the gel and subjected to the second PCR.The final products were cloned and sequenced. Their lengthes … More were 408,475,474 and 474 bp for the Hangzhou (China), Fukuoka (Japan), Tsushima Island (Japan) and Taegu (Korea) specimens, respectively. In all B.mandarina individuals tested, the nucleotide sequence were highly conserved except for the the former half of intron (corresponded to 314 to 379 residues) and completely the same in the of specimen from Hangzhou (China), Fukuoka (Japan) and Tsushima Island (Japan) as to the exon arts. The sequence for the Taequ (Korea) individuals, however, was slightly altered at three sites in the nucleotide sequence. On the other hand intron 3 had the 66 bp-long retroposon-like sequence (314 to 379 residues) in the Japanese specimens from Fukuoka and Tsushima Island. It was not found in the Chinese individuals from Hangzhou. These were the confirmation of a previous report comparing a Japanese B.mandarina strain and a Chinese one. Interestingly, the Korean B.mandarina from Taegu possessed the insertion sequence. Polymerase cahin reaction analysis of the arylphorin gene showed that there is a 66 bp-long retroposon-like insertion in the B.mandarina specimens which had the chromosome number of 2n=54, n=27. On the other hand, the ones with 2n=56, n=28 did not have the retroposon-like insertion. In other words, the occurrence of the insertion coincided with the 2n=54, n=27 chromosome number.A transposon-like insertion of a gene was recognized in B.mandarina speciments from Tsushima Island (Japan), Fukuoka (Japan) and Taegu (Korea) but not in those from Hangzhou (China). The occurrence of the insertion consistently coincided with the 2n=54, n=27 chromosome configuration as far as analyzed in the present study. Previous hybridization analysis of nucleolus organizer indicated that the Japanese population of B.mandarina was defferent from the Chinese population and that B.mori had closer relationship to the Chinese than to the Japanese B.mandarina. The current analysis supported the inference that B.mandarina from Korea resembles that from Japan. Less