Idengaku zasshi最新文献

The categorization of naturally occurring inversions in Drosophila melanogaster made by Mettler et al. (1977) was re-examined through compilation of recent data from the world-wide investigations. Categorization was changed into 5 classes by adding a new class: Common cosmopolitan, Rare cosmopolitan, Quasi cosmopolitan, Endemic and Unique. Modifications were also proposed: (1) The Rare cosmopolitans were limited to the 3 inversions, In(3L)M, In(3R)C and In(3R)Mo, instead of 8 inversions originally included. (2) Ambiguity between Endemic and Unique was noted and discussed. Data were presented to show that repeated surveys of the usual scale in a natural population indeed detected Endemic inversions which otherwise would have been classified as Unique inversions. More recent data on Japanese natural populations were finally presented. The Common cosmopolitans but not the Rare and Quasi cosmopolitans clearly showed high frequencies in the south.

Large amounts of genetic variation for preferred temperature was uncovered in natural populations of Drosophila immigrans and D. virilis. On average, the former preferred 17.8 degrees C and the latter did 21.0 degrees C. Most variation in D. immigrans was found among isofemale lines within geographic populations, with no significant difference among geographic populations. Both intra- and inter-populational differentiation were significant in D. virilis. No geographic cline in preferred temperature was observed in either species. The distribution of flies on the temperature gradient indicates that the temperature selection of D. immigrans is stronger than that of in D. virilis.

The E. coli chromosome is known to carry at least five genes, each of which codes for a "D-E-A-D" box protein that is presumed to possess an ATP-dependent RNA helicase activity. Four of such genes (srmB, deaD, dbpA and rhlB) were already mapped on the E. coli chromosome and their DNA sequences determined. We here report the complete nucleotide sequence of the remaining rhlE gene located at about 17.8 min on the E. coli genetic map. RhlE protein possesses all of the motifs (I to VI) conserved among prokaryotic and eukaryotic "D-E-A-D" proteins and has an arginine-rich carboxyl-terminal region. A null mutant of the rhlE gene was constructed by a new method with a ColE1 plasmid mutant that replicates in RNAse HI-deficient bacterial strains, but not in the wild-type strains. The delta rhlE mutant can grow normally, implying that the rhlE gene product is nonessential for bacterial cell growth.

DNA polymerase beta (pol beta) cDNA of rat fused to an enhancer-promoter region plus a poly(A) signal sequence of actin 5C gene of Drosophila (abbreviated pol beta) was transferred to the Drosophila genome. Three of four constructed transgenic strains possessing transgene pol beta on different chromosomes were studied. Levels of the pol beta transcript and those of the polymerization activity of pol beta were markedly elevated in cultured cells transfected with pol beta-bearing vectors as well as in embryos of the transgenic strains. The popular idea that DNA polymerase beta participates in DNA repair was not supported by the observation that a pair of a normal and a pol beta strain, and the other pair of a mei-9 mei-41 (DNA-repair deficient double mutations) strain and a pol beta mei-9 mei-41 strain, showed no difference in survival within each pair after treatment with ultraviolet light, methylmethane sulfonate and mitomycin C. The other idea that DNA polymerase beta participates in recombination was supported by the findings that spontaneous frequency of recombination, either meiotic or mitotic, is significantly higher in a transgenic pol beta strain than in a non-transgenic strain. The enhanced recombination frequency in the pol beta strain may, however, reflect an indirect effect of over-produced pol beta proteins on chromosomal stability. Whatever the direct effect of rat pol beta is, the transgenic pol beta flies will be useful for study of the physiological role of pol beta and the mechanism of recombination.

The genetic structure of temperature preference of D. immigrans was analyzed by a 4 x 4 diallel cross. Preference for low temperature was dominant to that for high temperature. Partition of the variance showed that most of the variance was additive; the variance caused by dominance was small but significant, and non-additive, non-dominance variance was not significant. Heritability of the temperature preference was 0.81. There may be a few genes involved in variation for temperature preference.

Spontaneous mutations were accumulated for a total of 1,678,388 allele-generations in several hundred replicate second chromosome lines. These lines were compared of a Cy chromosome and one of three different lethal bearing chromosomes from natural populations. Electrophoretic mobility and/or activity change was screened for seven enzyme loci. Forty-four null mutations were detected, but no band-morph mutations were observed. There is significant variation in null mutation rate among enzyme loci and among lethal chromosomes. This may be attributable to differences in the distribution of transposable elements among the lines. The band-morph mutation rate is pooled with previous results and becomes 7.48 x 10(-7) with a 95% confidence limit of 2.04 x 10(-7) to 1.91 x 10(-6) per locus per generation. Similarly, the pooled null mutation rate becomes 1.30 x 10(-5) with 95% confidence limit of 1.15 x 10(-5) to 1.52 x 10(-5) per locus per generation.

Available genetic data reveals that the human population is more variable than the chimpanzee population at the protein level, whereas the opposite is the case at the DNA level. The lower level of silent polymorphism in the human population suggests that its long-term breeding size is smaller than the chimpanzee's. The neutral theory suggests that natural selection has been relaxed in the human population under the improved environment. The possibility that the relaxation began with the emergence of Homo sapiens is examined, because it is known that H. habilis underwent for the first time dramatic changes in brain size, way of life, and culture, and that the childhood of H. erectus was already twice as long as that of chimpanzee. The relaxation hypothesis predicts that, relative to chimpanzee, some 20% of deleterious mutations became harmless under the changed environment throughout the Pleistocene. More extensive study of genetic variation in non-human primates is necessary not only to confirm the hypothesis, but also to better understand the human genome itself.

Repeated sequences are found ubiquitously in the eukaryotic genome. Population genetic studies on the evolution of such repeated sequences are reviewed while paying special attention to those sequences found in the non-coding regions of the genome. Specifically, the evolution of dispersed repeated sequences by the transposition as well as the evolution of short tandemly repeated sequences due to either replication slippage or unequal sister chromatid exchange are considered. The approach of combining both model and data analyses which has been successfully employed in the development of the neutral theory is also considered to be useful in better understanding the evolution and biological meaning of these sequences.

A large amount of genetic variation can be maintained in natural populations. In order to understand the mechanism maintaining genetic variation, we must first estimate the amount of genetic variation. There are two measures for estimating the amount of DNA polymorphism, i.e., the average number of pairwise nucleotide differences and the number of segregating sites among a sample of DNA sequences. Using these two measures, we can test the neutral mutation-random drift hypothesis (the neutral theory). The expectation of the amount of DNA polymorphism has been studied under several models, including population subdivision, change in population size, and natural selection. When a population is subdivided, a large amount of DNA polymorphism can be maintained in the population if the migration rates among subpopulations are small. In this case the amount of DNA polymorphism in the subpopulation with lower migration rate is expected to be smaller than that of higher migration rate. When the population size changes, the number of segregating sites changes more rapidly than does the average number of nucleotide differences. When purifying selection is operating, the number of segregating sites is more strongly affected by the existence of deleterious mutants than is the average number of nucleotide differences. On the other hand, when balancing selection is operating, the effect of the selection on the average number of nucleotide differences is larger than that on the number of segregating sites. A mutant under natural selection affects the amount of DNA polymorphism at linked sites (hitchhiking effect). DNA sequences are not random sequences and there may be conservative and variable regions in them. A statistical method for determining the window size and for finding nonrandom regions in the sequence is also presented.

The retinoblastoma 1 gene was assigned to mouse chromosome 14 at band D3 and rat chromosome 15 at band q12, respectively, by fluorescence in situ hybridization (FISH). These results suggest the syntenic association between human 13q14, mouse 14D3 and rat 15q12.