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61.
Andreyev AN Huyse M Van Duppen P Weissman L Ackermann D Gerl J Hessberger FP Hofmann S Kleinbohl A Munzenberg G Reshitko S Schlegel C Schaffner H Cagarda P Matos M Saro S Keenan A Moore C O'Leary CD Page RD Taylor M Kettunen H Leino M Lavrentiev A Wyss R Heyde K 《Nature》2000,405(6785):430-433
Understanding the fundamental excitations of many-fermion systems is of significant current interest. In atomic nuclei with even numbers of neutrons and protons, the low-lying excitation spectrum is generally formed by nucleon pair breaking and nuclear vibrations or rotations. However, for certain numbers of protons and neutrons, a subtle rearrangement of only a few nucleons among the orbitals at the Fermi surface can result in a different elementary mode: a macroscopic shape change. The first experimental evidence for this phenomenon came from the observation of shape coexistence in 16O (ref. 4). Other unexpected examples came with the discovery of fission isomers and super-deformed nuclei. Here we find experimentally that the lowest three states in the energy spectrum of the neutron deficient nucleus 186Pb are spherical, oblate and prolate. The states are populated by the alpha-decay of a parent nucleus; to identify them, we combine knowledge of the particular features of this decay with sensitive measurement techniques (a highly efficient velocity filters with strong background reduction, and an extremely selective recoil-alpha-electron coincidence tagging methods). The existence of this apparently unique shape triplet is permitted only by the specific conditions that are met around this particular nucleus. 相似文献
62.
Additional deletion in sex-determining region of human Y chromosome resolves paradox of X,t(Y;22) female 总被引:9,自引:0,他引:9
Whether a human embryo develops as a male or a female is determined by the presence of the Y chromosome. The sex-determining function lies entirely in interval 1A, inasmuch as most XX individuals with descended testes and normal male external genitalia carry this small region of the Y chromosome. We have localized an essential part of the sex-determining function to a portion of interval 1A, on the basis of the discovery of a female with a reciprocal Y;22 translocation and part of 1A deleted at the translocation breakpoint. Recently, a paradox has arisen with the report of four partially masculinized XX individuals who carry only a portion of interval 1A--a portion that does not overlap the deletion in the X,t(Y;22) female. These recent findings imply that the sex-determining function lies in the portion of 1A present in the four XX intersexes and not in the portion deleted in the X,t(Y;22) female. To explain the X,t(Y;22) individual, it was proposed that she was female because of a chromosomal position effect or delayed development of the gonadal soma. Here we report that the X,t(Y;22) female has a deletion of a second portion of interval 1A--a portion corresponding closely to that present in the XX intersexes. This resolves the apparent contradiction. Nonetheless, phenotype-genotype correlations suggest that two or more genetic elements in interval 1A may contribute to the sex-determining function of the Y chromosome. The X,t(Y;22) female lacks the ZFY gene but does not exhibit the complex phenotype known as Turner's syndrome, arguing against the hypothesis that ZFY is the Turner's syndrome gene on the Y chromosome. 相似文献
63.
64.
Racusin JL Karpov SV Sokolowski M Granot J Wu XF Pal'shin V Covino S van der Horst AJ Oates SR Schady P Smith RJ Cummings J Starling RL Piotrowski LW Zhang B Evans PA Holland ST Malek K Page MT Vetere L Margutti R Guidorzi C Kamble AP Curran PA Beardmore A Kouveliotou C Mankiewicz L Melandri A O'Brien PT Page KL Piran T Tanvir NR Wrochna G Aptekar RL Barthelmy S Bartolini C Beskin GM Bondar S Bremer M Campana S Castro-Tirado A Cucchiara A Cwiok M D'Avanzo P D'Elia V Valle MD de Ugarte Postigo A 《Nature》2008,455(7210):183-188
Long-duration gamma-ray bursts (GRBs) release copious amounts of energy across the entire electromagnetic spectrum, and so provide a window into the process of black hole formation from the collapse of massive stars. Previous early optical observations of even the most exceptional GRBs (990123 and 030329) lacked both the temporal resolution to probe the optical flash in detail and the accuracy needed to trace the transition from the prompt emission within the outflow to external shocks caused by interaction with the progenitor environment. Here we report observations of the extraordinarily bright prompt optical and gamma-ray emission of GRB 080319B that provide diagnostics within seconds of its formation, followed by broadband observations of the afterglow decay that continued for weeks. We show that the prompt emission stems from a single physical region, implying an extremely relativistic outflow that propagates within the narrow inner core of a two-component jet. 相似文献
65.
Soderberg AM Berger E Page KL Schady P Parrent J Pooley D Wang XY Ofek EO Cucchiara A Rau A Waxman E Simon JD Bock DC Milne PA Page MJ Barentine JC Barthelmy SD Beardmore AP Bietenholz MF Brown P Burrows A Burrows DN Bryngelson G Byrngelson G Cenko SB Chandra P Cummings JR Fox DB Gal-Yam A Gehrels N Immler S Kasliwal M Kong AK Krimm HA Kulkarni SR Maccarone TJ Mészáros P Nakar E O'Brien PT Overzier RA de Pasquale M Racusin J Rea N York DG 《Nature》2008,453(7194):469-474
Massive stars end their short lives in spectacular explosions--supernovae--that synthesize new elements and drive galaxy evolution. Historically, supernovae were discovered mainly through their 'delayed' optical light (some days after the burst of neutrinos that marks the actual event), preventing observations in the first moments following the explosion. As a result, the progenitors of some supernovae and the events leading up to their violent demise remain intensely debated. Here we report the serendipitous discovery of a supernova at the time of the explosion, marked by an extremely luminous X-ray outburst. We attribute the outburst to the 'break-out' of the supernova shock wave from the progenitor star, and show that the inferred rate of such events agrees with that of all core-collapse supernovae. We predict that future wide-field X-ray surveys will catch each year hundreds of supernovae in the act of exploding. 相似文献
66.
High mutation rates have driven extensive structural polymorphism among human Y chromosomes 总被引:15,自引:0,他引:15
Repping S van Daalen SK Brown LG Korver CM Lange J Marszalek JD Pyntikova T van der Veen F Skaletsky H Page DC Rozen S 《Nature genetics》2006,38(4):463-467
Although much structural polymorphism in the human genome has been catalogued, the kinetics of underlying change remain largely unexplored. Because human Y chromosomes are clonally inherited, it has been possible to capture their detailed relationships in a robust, worldwide genealogical tree. Examination of structural variation across this tree opens avenues for investigating rates of underlying mutations. We selected one Y chromosome from each of 47 branches of this tree and searched for large-scale variation. Four chromosomal regions showed extensive variation resulting from numerous large-scale mutations. Within the tree encompassed by the studied chromosomes, the distal-Yq heterochromatin changed length > or = 12 times, the TSPY gene array changed length > or = 23 times, the 3.6-Mb IR3/IR3 region changed orientation > or = 12 times and the AZFc region was rearranged > or = 20 times. After determining the total time spanned by all branches of this tree (approximately 1.3 million years or 52,000 generations), we converted these mutation counts to lower bounds on rates: > or = 2.3 x 10(-4), > or = 4.4 x 10(-4), > or = 2.3 x 10(-4) and > or = 3.8 x 10(-4) large-scale mutations per father-to-son Y transmission, respectively. Thus, high mutation rates have driven extensive structural polymorphism among human Y chromosomes. At the same time, we found limited variation in the copy number of Y-linked genes, which raises the possibility of selective constraints. 相似文献
67.
Hughes JF Skaletsky H Rozen S Wilson RK Page DC 《Nature genetics》2006,38(8):853-4; author reply 854-5
68.
In germ cells of mouse embryonic ovaries, the decision to enter meiosis precedes premeiotic DNA replication 总被引:4,自引:0,他引:4
Baltus AE Menke DB Hu YC Goodheart ML Carpenter AE de Rooij DG Page DC 《Nature genetics》2006,38(12):1430-1434
The transition from mitosis to meiosis is a defining juncture in the life cycle of sexually reproducing organisms. In yeast, the decision to enter meiosis is made before the single round of DNA replication that precedes the two meiotic divisions. We present genetic evidence of an analogous decision point in the germ line of a multicellular organism. The mouse Stra8 gene is expressed in germ cells of embryonic ovaries, where meiosis is initiated, but not in those of embryonic testes, where meiosis does not begin until after birth. Here we report that in female embryos lacking Stra8 gene function, the early, mitotic development of germ cells is normal, but these cells then fail to undergo premeiotic DNA replication, meiotic chromosome condensation, cohesion, synapsis and recombination. Combined with previous findings, these genetic data suggest that active differentiation of ovarian germ cells commences at a regulatory point upstream of premeiotic DNA replication. 相似文献
69.
Hughes JF Skaletsky H Brown LG Pyntikova T Graves T Fulton RS Dugan S Ding Y Buhay CJ Kremitzki C Wang Q Shen H Holder M Villasana D Nazareth LV Cree A Courtney L Veizer J Kotkiewicz H Cho TJ Koutseva N Rozen S Muzny DM Warren WC Gibbs RA Wilson RK Page DC 《Nature》2012,483(7387):82-86
The human X and Y chromosomes evolved from an ordinary pair of autosomes during the past 200-300 million years. The human MSY (male-specific region of Y chromosome) retains only three percent of the ancestral autosomes' genes owing to genetic decay. This evolutionary decay was driven by a series of five 'stratification' events. Each event suppressed X-Y crossing over within a chromosome segment or 'stratum', incorporated that segment into the MSY and subjected its genes to the erosive forces that attend the absence of crossing over. The last of these events occurred 30 million years ago, 5 million years before the human and Old World monkey lineages diverged. Although speculation abounds regarding ongoing decay and looming extinction of the human Y chromosome, remarkably little is known about how many MSY genes were lost in the human lineage in the 25 million years that have followed its separation from the Old World monkey lineage. To investigate this question, we sequenced the MSY of the rhesus macaque, an Old World monkey, and compared it to the human MSY. We discovered that during the last 25 million years MSY gene loss in the human lineage was limited to the youngest stratum (stratum 5), which comprises three percent of the human MSY. In the older strata, which collectively comprise the bulk of the human MSY, gene loss evidently ceased more than 25 million years ago. Likewise, the rhesus MSY has not lost any older genes (from strata 1-4) during the past 25 million years, despite its major structural differences to the human MSY. The rhesus MSY is simpler, with few amplified gene families or palindromes that might enable intrachromosomal recombination and repair. We present an empirical reconstruction of human MSY evolution in which each stratum transitioned from rapid, exponential loss of ancestral genes to strict conservation through purifying selection. 相似文献
70.
A fundamental goal of sociobiology is to explain how complex social behaviour evolves, especially in social insects, the exemplars of social living. Although still the subject of much controversy, recent theoretical explanations have focused on the evolutionary origins of worker behaviour (assistance from daughters that remain in the nest and help their mother to reproduce) through expression of maternal care behaviour towards siblings. A key prediction of this evolutionary model is that traits involved in maternal care have been co-opted through heterochronous expression of maternal genes to result in sib-care, the hallmark of highly evolved social life in insects. A coupling of maternal behaviour to reproductive status evolved in solitary insects, and was a ready substrate for the evolution of worker-containing societies. Here we show that division of foraging labour among worker honey bees (Apis mellifera) is linked to the reproductive status of facultatively sterile females. We thereby identify the evolutionary origin of a widely expressed social-insect behavioural syndrome, and provide a direct demonstration of how variation in maternal reproductive traits gives rise to complex social behaviour in non-reproductive helpers. 相似文献