Transmission of male recombination,segregation distortion and sex-ratio imbalance inDrosophila melanogaster

From the first test cross progenies of control (no larval transfers; no ethyl methanesulphonate), physical stress (two larval transfers; no ethyl methanesulphonate) and 0.75% ethyl methanesulphonate (two larval transfers; 0.75% ethyl methanesulphonate)-treated F₁ (Oregon K +/dumpy black cinnabar, dp b cn) males ofDrosophila melanogaster, respectively, 6,10 and 52 wild-looking first test cross males were again test crossed to obtain second generation. The overall percentages of male recombination detected in the second test cross progenies, in the three sets of experiments, were statistically the same as those in the first test cross progenies. Thus the enhanced male recombination caused by physical stress (with or without ethyl methanesulphonate) was transmitted to next generation. Non-reciprocal male recombination was observed indp b but not inb cn region in both first and second test cross progenies. Three abnormalities, (i) production of wild-type flies in majority overdp b cn type, (ii) Non-Mendelian segregation atdp b andcn loci and (iii) sex-ratio differences fordp bcn and +b cn types observed in test cross progenies of F₁ males ofDrosophila melanogaster were transmitted to next generation when induced with 0.75 % ethyl methanesulphonate but not when these abnormalities were induced with physical stress. The data suggest possible association of non-reciprocal male recombination, segregation distortion and sex-ratio imbalance inDrosophila melanogaster. In fact these may be representing different aspects of the same phenomenon     

Ovulation suppression protects against chromosomal abnormalities in mouse eggs at advanced maternal age

1. Download : Download high-res image (270KB)
2. Download : Download full-size image

     

Genetic variation,inheritance, and quaternary structure of malic enzyme in brook trout (Salvelinus fontinalis)

Electrophoretic variation is described for malic enzyme (ME) for the first time in brook trout (Salvelinus fontinalis). Since the quaternary structure of ME was not clear from examination of banding patterns in brook trout alone, ME phenotypes in rainbow trout (Salmo gairdneri) × brook trout hybrids as well as in esocid species demonstrated that ME is tetrameric. A model of two duplicated loci is proposed to account for the observed variation. One locus (ME-2) is fixed and one locus (ME-1) is variable with three electrophoretically distinct alleles; the protein products of ME-1 are reduced in activity relative to the protein products of ME-2. Joint segregation was examined between ME-1 and ten other biochemical loci in brook trout, and between ME-1, ME-2, and nine other biochemical loci in a splake—lake trout (Salvelinus namaycush) × brook trout hybrid—backcross. All pairwise examinations showed random assortment except ME-2 with an isocitrate dehydrogenase locus (IDH-3), which showed complete linkage in the splake backcross. This may be due to a chromosomal aberration.Authorized for publication as Paper No. 5599 in the Journal Series of The Pennsylvania Agricultural Experiment Station, University Park, Pennsylvania, in cooperation with the Benner Spring Fish Research Station, The Pennsylvania Fish Commission, Bellefonte, Pennsylvania. M.S. was supported by an NSF Graduate Fellowship.     

Niche segregation in reptile ticks: attachment sites and reproductive success of females

Summary This study examined whether the mating or feeding success of females of two tick species, Amblyomma limbatum and Aponomma hydrosauri, is influenced by their site of attachment on a host. Marked interspecific differences were detected in the preferred sites of attachment of females to their common host, the sleepy lizard Tiliqua rugosa, with Amb. limbatum found predominantly in the ears and on the lower back, while Ap. hydrosauri preferred to attach under the forelimbs and on the midback. Data from field surveys suggested that higher proportions of females were mated in the preferred sites for Ap. hydrosauri, and in one of the preferred sites for Amb. limbatum. However, laboratory and field experiments showed that for both species, the mean time before females were mated, mean engorgement time and mean feeding rate were independent of where they were attached to a host. Four hypotheses were considered as explanations of the observed niche segregation; intespecific competition, avoidance of pheromone jamming or adaptations, to maximize mating and feeding, and minimize physical disturbance. These could not totally explain the observed site specificity in either tick species. Site specificity may represent adaptations by each species to other host species encountered within their distributional range.     

Human naive epiblast cells possess unrestricted lineage potential

1. Download : Download high-res image (172KB)
2. Download : Download full-size image

     

Chromosome Segregation and Peptidoglycan Remodeling Are Coordinated at a Highly Stabilized Septal Pore to Maintain Bacterial Spore Development

1. Download : Download high-res image (133KB)
2. Download : Download full-size image

     

Gene segregation in autotetraploids: prediction from meiotic configurations

Current systems of estimating gene segregation in autotetraploids usually are based on two extreme methods: chromosome segregation with absolute centromere linkage, or maximum equational segregation with crossing over always occurring between the centromeres and marker genes. The hiatus between the two methods is unacceptable quantitatively, and segregation of the d gene in tomato shows that neither method predicts an acceptable fit. We present a new meiotic configuration (MC) method of analyzing tetrasomic inheritance in autotetraploids that allows more accurate estimations of all intermediate types of segregation. The method is based on a maximum of two chiasmata per bivalent and four per quadrivalent. The theoretically expected numbers of bivalents and chain and circle quadrivalents are derived first. Chromosome frequencies from these configurations are then used to determine relative contributions from each configuration to the gamete genotypes by way of newly developed tables for gene segregation in various autotetraploid genotypes. The large sample sizes from classic 4x tomato (Solanum lycopersicum L.) data are used to demonstrate the stepwise method of calculating gamete genotypes, and the method gives acceptable fits for the data tested. The interspecific tetraploid hybrid Solanum lycopersicum × S. pimpinellifolium had good fits to expected autotetraploid segregation, supporting its autoploid nature and the fact that taxonomic rank should not be a consideration in designating categories of polyploids. Autotetraploid allozyme segregation data for several genes in one genus of another family had acceptable and usually better fits to the MC expectations than to the standard methods.     

Reproductive Ecology and Host Utilization of Four Sympatric Bitterling (Acheilognathinae,Cyprinidae) in a Lowland Reach of the Harai River in Mie,Japan

Bitterling are fishes that use freshwater mussels for oviposition. The reproductive ecology and pattern of mussel utilization of four sympatric species of bitterling, Acheilognathus rhombeus, A. tabira tabira, Tanakia lanceolata, and T. limbata, were investigated in a lowland river with seven sympatric mussel species. Three bitterling species are spring spawners with overlapping spawning seasons. A. rhombeus is an autumn-spawning species and is temporally isolated in its reproduction from the other species. Ovipositor length during oviposition of T. limbata and T. lanceolata was short, while those of A. tabira tabira and A. rhombeus were long. Most T. limbata inhabited near-shore areas, whereas the two other spring-spawning species were distributed across the entire river. All bitterling species used Inversidens brandti, Obovalis omiensis and Inversiunio jokohamensis as spawning hosts, but not the other mussel species available. T. lanceolata, A. tabira tabira and A. rhombeus showed spawning preferences for O. omiensis and I. brandti. However, T. limbata did not show clear preferences for any of the mussel species they used. A. t. tabira showed a significant preference for large I. brandti in offshore areas, while the other spring-spawning bitterling showed a preference for mussels inshore. These results are discussed in the context of reproductive resource partitioning.     

SIZE-CLASS SEGREGATION OF BOWHEAD WHALES DISCERNED THROUGH AERIAL STEREOPHOTOGRAMMETRY

Bowhead whales ( Balaena mysticetus ) summering in the eastern Beaufort Sea in 1983 were measured through aerial stereophotogrammetry. Photos were taken from a turbine Aerocommander 690 with wingtip-mounted, calibrated 35-mm cameras. Photos were measured on an analytical plotter with scale data provided by radar altimeter and focal length of the lenses. Coefficient of variation of known-sized targets 12 m long was 1.7 percent ( n = 25). Potential duplicate photographs of whales were removed from consideration through an algorithm based on whale swim speed and elapsed time between sightings. Significant segregation by bowhead whale length was found between four broad regions ( P < 0.001, ANOVA, Chi square). Also an inverse correlation appeared between longitude and size of animals ( P < 0.001), with the larger animals occurring farther east. This unequivocal size-class segregation confounds an accurate assessment of overall size-class composition of the population as well as recent attempts to determine calving rate from aerial survey data.     

The budding yeast kinetochore: less simple than expected

Summary We focus on the established kinetochore proteins of the budding yeast,Saccharomyces cerevisiae. The location and functional evidence for each kinetochore protein is summarized along with the data that supports protein-protein and genetic interactions. Models are proposed to illustrate how these kinetochore proteins assemble to evoke a kinetochore-centromere complex.