Masa-Aki Yamada

Multiplication of 28S rDNA and NOR activity in chromosome evolution among ants of the Myrmecia pilosula species complex

AbstractChromosomal localization of rDNA in samples of five taxa of the Myrmecia pilosula species complex (Hymeoptera: Formicidae: Myrmeciinae) with 2n=3 (M. croslandi), 8 (M. imaii), 10 (M. banksi), 18 (M. haskinsorum), and 27 (M. pilosula) was carried out by fluorescence in situ hybridization (FISH) using cloned M. croslandi rDNA (pMc.r2) including the coding region for 28S rRNA. Results show that (1) the 28S rDNA in the genome of these ants is repetitive and is localized in pericentromeric C-bands, (2) the number of chromosomes carrying rDNA is two in M. croslandi, M. imaii and M. banksi, six in M. haskinsorum and ten in M. pilosula, and (3) only one or two clusters of rRNA genes generate nucleoli in each species. We suggest that the rDNA in the ancestral stock of the M. pilosula complex was localized originally in a pericentromeric C-band, and multiplied by chance with time during saltatory increases in C-banding following episodes of centric fission. Most rDNA multiplied on various chromosomes seems to be inactivated and eliminated from the genome, together with C-bands, by

HEREDITARY CHANGE IN BOMBYX AFTER TREATMENT WITH DNA

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HEREDITARY CHANGES IN CAPSICUM ANNUUM L.

-inversion or centric fusion, with the remnant rDNAs dispersed in the genome by centric fission and

Cloning of the plasmids in cytoplasmic male sterile rice and changes of organization of mitochondrial and nuclear DNA in cytoplasmic reversion

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EFFECTS OF SR FACTOR AND DA GENE ON THE VIABILITY OF THE HYBRID BETWEEN DROSOPHILA MELANOGASTER AND D. SIMULANS

-inversion.

DNA-INDUCED TRANSFORMATION IN SILKWORM

The present study was carried out to examine the genetic mechanism responsible for reversions to fertile phenotype detected in cytoplasmic male-sterile plants of rice. The cms-bo cytoplasm of Chinsurah boro II gave rise to male-sterility in plants without a gametophytic restorer gene (/?/i). Taichung 65 (T65A) was known to be the maintainer which carries no restorer; however, Taichung 65 preserved in our laboratory (T65B) showed partial fertility (about 8 % seed set) when crossed with the male-sterile plants. Unexpectedly, the seed fertility gradually increased with repeated selfings and almost fully fertile plants were obtained in the F6 generation. The cytoplasmic substitution lines revealed that reversions to fertile phenotype resulted from mutational events at the nuclear level. The genetic experiments indicated that the partial fertility observed in the F1 hybrid was controlled by a dominant gene, Ifrv which was carried by T65B. The results obtained suggested that Ifr1 itself was associated with instability of fertility restoration in the presence of cms-bo cytoplasm since partially fertile plants carrying Ifrl always showed a tendency for gradual increase in fertility in the later generations. The results are also discussed in relation to a rapid genetic change through intensified gametic selection combined with instability.