Abstract
Two types (R a1 and R a2) of nucleolus organizers were identified in the genome of Bombyx mandarina (Japan) which occurs in Japan. Genetical analysis of a hybrid with B. mori suggested that the loci of both nucleolus organizers are allelic and correspond to the R 0 locus of B. mori. These nucleolus organizers segregated and were inherited by the progeny in a Mendelian fashion. The majority of the R a1 rDNA units were 10.6 kb in length and had an additional EcoRI site in the transcribed spacer region when compared with the same size unit of R 0. On the other hand, the KpnI site present in the non-transcribed spacer region of the R 0 rDNA was not detected in the R a1 unit. The 15.1 kb unit observed in the R a2 locus was the same as the unit with the type II intron of R 0. The four major components of R a2 rDNA, with lengths of 10.6, 15.1, 15.7 and 20.8 kb, were also found in the R 0 locus, and thus the R a2 and the R 0 loci were considered to be closely related. Usually the functional unit of rDNA in the nucleolus organizers of homologous or non-homologous chromosomes cannot be easily distinguished. However, in the case of B. mandarina (Japan), distinct functional 10.6 kb units were observed in the allelic R a1 and R a2 loci. Therefore the existence of the two distinct units suggest the possibility of introducing the chromosomes of the interspecies in the genus Bombyx.
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Maekawa, H., Takada, N., Mikitani, K. et al. Nucleolus organizers in the wild silkworm Bombyx mandarina and the domesticated silkworm B. mori . Chromosoma 96, 263–269 (1988). https://doi.org/10.1007/BF00286912
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DOI: https://doi.org/10.1007/BF00286912