Search

Tensile testing may be used to decide, say, which steel to use in various constructions. Analogous testing can be done simply in the classroom using plasticine and helps to introduce pupils to the various properties studied in materials science.

The gene expression level across the entire genomes of males and females was examined using microarray expression profiles. The striking associations of sex-biased gene expression were reported with the X chromosome.

This study provides a morphological, ultrastructural, and phylogenetic characterization of a novel micro‐eukaryotic parasite (2.3–2.6 µm) infecting amphipod genera Echinogammarus and Orchestia. Longitudinal studies across two years revealed that infection prevalence peaked in late April and May, reaching 64% in Echinogammarus sp. and 15% in Orchestia sp., but was seldom detected during the rest of the year. The parasite infected predominantly hemolymph, connective tissue, tegument, and gonad, although hepatopancreas and nervous tissue were affected in heavier infections, eliciting melanization and granuloma formation. Cell division occurred inside walled parasitic cysts, often within host hemocytes, resulting in hemolymph congestion. Small subunit (18S) rRNA gene phylogenies including related environmental sequences placed the novel parasite as a highly divergent lineage within Class Filasterea, which together with Choanoflagellatea represent the closest protistan relatives of Metazoa. We describe the new parasite as Txikispora philomaios n. sp. n. g., the first confirmed parasitic filasterean lineage, which otherwise comprises four free‐living flagellates and a rarely observed endosymbiont of snails. Lineage‐specific PCR probing of other hosts and surrounding environments only detected T. philomaios in the platyhelminth Procerodes sp. We expand the known diversity of Filasterea by targeted searches of metagenomic datasets, resulting in 13 previously unknown lineages from environmental samples. [ABSTRACT FROM AUTHOR]

Polymerase δ‐interacting protein 2 (POLDIP2, PDIP38) is a multifaceted, "moonlighting" protein, involved in binding protein partners from many different cellular processes, including mitochondrial metabolism and DNA replication and repair. How POLDIP2 interacts with many different proteins is unknown. Towards this goal, we present the crystal structure of POLDIP2 to 2.8 Å, which exhibited a compact two‐domain β‐strand‐rich globular structure, confirmed by circular dichroism and small angle X‐ray scattering approaches. POLDIP2 comprised canonical DUF525 and YccV domains, but with a conserved domain linker packed tightly, resulting in an "extended" YccV module. A central channel was observed, which we hypothesize could influence structural changes potentially mediated by redox conditions, following observation of a modified cysteine residue in the channel. Unstructured regions were rebuilt by ab initio modelling to generate a model of full‐length POLDIP2. Molecular dynamics simulations revealed a highly dynamic N‐terminal region tethered to the YccV‐domain by an extended linker, potentially facilitating interactions with distal binding partners. Models of POLDIP2 complexed with two of its partners, PrimPol and PCNA, indicated that dynamic flexibility of the POLDIP2 N‐terminus and loop regions likely mediate protein interactions. PDB Code(s): 6Z9C; [ABSTRACT FROM AUTHOR]

The stalk-eyed flies (Diopsidae, Diptera) are a family of approximately 100 species of calypterate dipterans, characterised by extended head capsules. Species within the family have previously been shown to possess six subfamilies of mariner transposons, with nucleotide substitution patterns suggesting that at least two subfamilies are currently active. The vertumnana subfamily has been shown to have been involved in a horizontal transfer event involving Diopsidae and a second dipteran family in the Tephritidae. Presented here are cloned and sequenced mariner elements from three further diopsid species, in addition to a bioinformatic analysis of mariner elements identified in transcriptomic and genomic data from the genus Teleopsis. The newly identified mariner elements predominantly fall into previously recognised subfamilies, however the publicly available Teleopsis data also revealed a novel subfamily. Three of the seven identified subfamilies are shown to have undergone horizontal transfer, two of which appear to involve diopsid donor species. One recipient group of a diopsid mariner is the Bactrocera genus of tephritid flies, the transfer of which was previously proposed in an earlier study of diopsid mariner elements. The second horizontal transfer, of the mauritiana subfamily, can be traced from the Teleopsis genus to the cnidarian Hydra vulgaris. The mauritiana elements are shown to be active in the recipient H. vulgaris and transposase expression is observed in all body tissues examined in both species. The increased diversity of diopsid mariner elements points to a minimum of four subfamilies being present in the ancestral genome. Both vertical inheritance and stochastic loss of TEs have subsequently occurred within the diopsid radiation. The TE complement of H. vulgaris contains at least two mariner subfamilies of insect origin. Despite the phylogenetic distance between donor and recipient species, both subfamilies are shown to be active and proliferating within H. vulgaris. [ABSTRACT FROM AUTHOR]

Choanoflagellates and filastereans are the closest known single celled relatives of Metazoa within Holozoa and provide insight into how animals evolved from their unicellular ancestors. Codon usage bias has been extensively studied in metazoans, with both natural selection and mutation pressure playing important roles in different species. The disparate nature of metazoan codon usage patterns prevents the reconstruction of ancestral traits. However, traits conserved across holozoan protists highlight characteristics in the unicellular ancestors of Metazoa. Presented here are the patterns of codon usage in the choanoflagellates Monosiga brevicollis and Salpingoeca rosetta, as well as the filasterean Capsaspora owczarzaki. Codon usage is shown to be remarkably conserved. Highly biased genes preferentially use GC-ending codons, however there is limited evidence this is driven by local mutation pressure. The analyses presented provide strong evidence that natural selection, for both translational accuracy and efficiency, dominates codon usage bias in holozoan protists. In particular, the signature of selection for translational accuracy can be detected even in the most weakly biased genes. Biased codon usage is shown to have coevolved with the tRNA species, with optimal codons showing complementary binding to the highest copy number tRNA genes. Furthermore, tRNA modification is shown to be a common feature for amino acids with higher levels of degeneracy and highly biased genes show a strong preference for using modified tRNAs in translation. The translationally optimal codons defined here will be of benefit to future transgenics work in holozoan protists, as their use should maximise protein yields from edited transgenes. [ABSTRACT FROM AUTHOR]

Aims: Bacteria are considered one of the major driving forces of the mammalian decomposition process and have only recently been recognised as forensic tools. At this point, little is known about their potential use as 'post-mortem clocks'. This study aimed to establish the proof of concept for using bacterial identification as post-mortem interval (PMI) indicators, using a multi-omics approach.Methods and Results: Pieces of pork were placed in the University's outdoor facility and surface swabs were taken at regular intervals up to 60 days. Terminal restriction fragment length polymorphism (T-RFLP) of the 16S rDNA was used to identify bacterial taxa. It succeeded in detecting two out of three key contributors involved in decomposition and represents the first study to reveal Vibrionaceae as abundant on decomposing pork. However, a high fraction of present bacterial taxa could not be identified by T-RFLP. Proteomic analyses were also performed at selected time points, and they partially succeeded in the identification of precise strains, subspecies and species of bacteria that colonized the body after different PMIs.Conclusion: T-RFLP is incapable of reliably and fully identifying bacterial taxa, whereas proteomics could help in the identification of specific strains of bacteria. Nevertheless, microbial identification by next generation sequencing might be used as PMI clock in future investigations and in conjunction with information provided by forensic entomologists.Significance and Impact Of the Study: To the best of our knowledge, this work represents the first attempt to find a cheaper and easily accessible, culture-independent alternative to high-throughput techniques to establish a 'microbial clock', in combination with proteomic strategies to address this issue. [ABSTRACT FROM AUTHOR]

Recent advances in molecular technology have revolutionized research on all aspects of the biology of organisms, including ciliates, and created unprecedented opportunities for pursuing a more integrative approach to investigations of biodiversity. However, this goal is complicated by large gaps and inconsistencies that still exist in the foundation of basic information about biodiversity of ciliates. The present paper reviews issues relating to the taxonomy of ciliates and presents specific recommendations for best practice in the observation and documentation of their biodiversity. This effort stems from a workshop that explored ways to implement six Grand Challenges proposed by the International Research Coordination Network for Biodiversity of Ciliates ( IRCN- BC). As part of its commitment to strengthening the knowledge base that supports research on biodiversity of ciliates, the IRCN- BC proposes to populate The Ciliate Guide, an online database, with biodiversity-related data and metadata to create a resource that will facilitate accurate taxonomic identifications and promote sharing of data. [ABSTRACT FROM AUTHOR]

Recent studies have shown that molecular phylogenies of the choanoflagellates (Class Choanoflagellatea) are in disagreement with their traditional taxonomy, based on morphology, and that Choanoflagellatea requires considerable taxonomic revision. Furthermore, phylogenies suggest that the morphological and ecological evolution of the group is more complex than has previously been recognized. Here we address the taxonomy of the major choanoflagellate order Craspedida , by erecting four new genera. The new genera are shown to be morphologically, ecologically and phylogenetically distinct from other choanoflagellate taxa. Furthermore, we name five novel craspedid species, as well as formally describe ten species that have been shown to be either misidentified or require taxonomic revision. Our revised phylogeny, including 18 new species and sequence data for two additional genes, provides insights into the morphological and ecological evolution of the choanoflagellates. We examine the distribution within choanoflagellates of these two additional genes, EF-1A and EFL, closely related translation GTPases which are required for protein synthesis. Mapping the presence and absence of these genes onto the phylogeny highlights multiple events of gene loss within the choanoflagellates. [ABSTRACT FROM AUTHOR]

• The previously unresolved root of Acanthoecida is identified. • Rare genomic changes support the proposed root. • Codon bias is identified as a putative source of artefactual phylogenetic signals. • The tectiform family Stephanoecidae appears to be an invalid taxon. Lorica-bearing choanoflagellates belong to the order Acanthoecida, a taxon which has been consistently recovered as monophyletic in molecular phylogenies. Based upon differences in lorica development and morphology, as well as the presence or absence of a motile dispersal stage, species are labelled as either nudiform or tectiform. Whilst Acanthoecida is robustly resolved in molecular phylogenies, the placement of the root of the clade is less certain with two different positions identified in past studies. One recovered root has been placed between the nudiform family Acanthoecidae and the tectiform family Stephanoecidae. An alternative root placement falls within the tectiform species, recovering the monophyletic Acanthoecidae nested within a paraphyletic Stephanoecidae. Presented here is a 14-gene phylogeny, based upon nucleotide and amino acid sequences, which strongly supports tectiform paraphyly. The horizontal transfer of a ribosomal protein gene, from a possible SAR donor, into a subset of acanthoecid species provides further, independent, support for this root placement. Differing patterns of codon usage bias across the choanoflagellates are proposed as the cause of artefactual phylogenetic signals that lead to the recovery of tectiform monophyly. [ABSTRACT FROM AUTHOR]

• Complete silicon starvation of tectiform Stephanoeca diplocostata results in diagonal (nudiform) division. • Silicon-replenished S. diplocostata cells accumulate costal strips in a nudiform manner. • 'Nudiform loricae' assembled on silicon-replenished cells display variations with respect to the transverse costae. • Newly identified nudiform genus Enibas possesses Stephanoeca -like loricae with similarities to nudiform loricae of S. diplocostata. • Suggested that morphological similarities together with recent phylogenetic analyses could imply Enibas species had a Stephanoeca -like ancestor. The deposition of silicified costal strips and lorica assembly in choanoflagellates is precisely linked to the cell cycle. A minority of species undergo nudiform division whereby a loricate cell divides to produce a naked daughter cell that deposits a set of costal strips and then assembles a lorica. Most species undergo tectiform division whereby a parent loricate cell produces a set of costal strips, divides and passes on the stored strips to a daughter cell that immediately assembles a lorica. Many phylogenetic analyses recover nudiform and tectiform species as sister-clades giving the impression that they are distinct evolutionary lineages. However, the tectiform species Stephanoeca diplocostata is capable of undergoing nudiform division and depositing costal strips and assembling a lorica with certain modifications in a nudiform manner. The recent discovery of a new genus, Enibas, comprising species with Stephanoeca -like loricae that undergo nudiform cell division and on phylogenetic analysis occur as a sister group to other nudiform species has drawn attention to whether there are also unique features in lorica construction. A range of Enibas loricae is illustrated and it appears that there are unique features which might be interpreted as being derived from a Stephanoeca -like ancestor. [ABSTRACT FROM AUTHOR]

Capsaspora owczarzaki, a protistan symbiont of the pulmonate snail Biomphalaria glabrata, is the centre of much interest in evolutionary biology due to its close relationship to Metazoa. The whole genome sequence of this protist has revealed new insights into the ancestral genome composition of Metazoa, in particular with regard to gene families involved in the evolution of multicellularity. The draft genome revealed the presence of 23 families of transposable element, made up from DNA transposon as well as long terminal repeat (LTR) and non-LTR retrotransposon families. The phylogenetic analyses presented here show that all of the transposable elements identified in the C. owczarzaki genome have orthologous families in Metazoa, indicating that the ancestral metazoan also had a rich diversity of elements. Molecular evolutionary analyses also show that the majority of families has recently been active within the Capsaspora genome. One family now appears to be inactive and a further five families show no evidence of current transposition. Most individual element copies are evolutionarily young; however, a small proportion of inserts appear to have persisted for longer in the genome. The families present in the genome show contrasting population histories and appear to be in different stages of their life cycles. Transcriptome data have been analyzed from multiple stages in the C. owczarzaki life cycle. Expression levels vary greatly both between families and between different stages of the life cycle, suggesting an unexpectedly complex level of transposable element regulation in a single celled organism. [ABSTRACT FROM AUTHOR]

Background The GTPase eEF1A is the eukaryotic factor responsible for the essential, universal function of aminoacyl-tRNA delivery to the ribosome. Surprisingly, eEF1A is not universally present in eukaryotes, being replaced by the paralog EFL independently in multiple lineages. The driving force behind this unusually frequent replacement is poorly understood. Results Through sequence searching of genomic and EST databases, we find a striking association of eEF1A replacement by EFL and loss of eEF1A's guanine exchange factor, eEF1Bα, suggesting that EFL is able to spontaneously recharge with GTP. Sequence conservation and homology modeling analyses indicate several sequence regions that may be responsible for EFL's lack of requirement for eEF1Bα. Conclusions We propose that the unusual pattern of eEF1A, eEF1Bα and EFL presence and absence can be explained by a ratchet-like process: if either eEF1A or eEF1Bα diverges beyond functionality in the presence of EFL, the system is unable to return to the ancestral, eEF1A:eEFBα-driven state. [ABSTRACT FROM AUTHOR]

Saccharomyces cerevisiae is one of the premier model systems for studying the genomics and evolution of transposable elements. The availability of the S. cerevisiae genome led to unprecedented insights into its five known transposable element families (the LTR retrotransposons Ty1-Ty5) in the years shortly after its completion. However, subsequent advances in bioinformatics tools for analysing transposable elements and the recent availability of genome sequences for multiple strains and species of yeast motivates new investigations into Ty evolution in S. cerevisiae. Here we provide a comprehensive phylogenetic and population genetic analysis of all Ty families in S. cerevisiae based on a systematic re-annotation of Ty elements in the S288c reference genome. We show that previous annotation efforts have underestimated the total copy number of Ty elements for all known families. In addition, we identify a new family of Ty3-like elements related to the S. paradoxus Ty3p which is composed entirely of degenerate solo LTRs. Phylogenetic analyses of LTR sequences identified three families with short-branch, recently active clades nested among long branch, inactive insertions (Ty1, Ty3, Ty4), one family with essentially all recently active elements (Ty2) and two families with only inactive elements (Ty3p and Ty5). Population genomic data from 38 additional strains of S. cerevisiae show that the majority of Ty insertions in the S288c reference genome are fixed in the species, with insertions in active clades being predominantly polymorphic and insertions in inactive clades being predominantly fixed. Finally, we use comparative genomic data to provide evidence that the Ty2 and Ty3p families have arisen in the S. cerevisiae genome by horizontal transfer. Our results demonstrate that the genome of a single individual contains important information about the state of TE population dynamics within a species and suggest that horizontal transfer may play an important role in shaping the genomic diversity of transposable elements in unicellular eukaryotes. [ABSTRACT FROM AUTHOR]

ABSTRACT. The choanoflagellates (Choanoflagellatea) comprise a major group of nanoflagellates, which are ubiquitous in the aquatic environment. Recent molecular phylogenies have shown them to be the sister group to the Metazoa. However, the phylogeny of the choanoflagellates is still far from understood. We present here a 29 taxon, multigene phylogeny that robustly places the root of the choanoflagellates. One of the original nonloricate families, Codonosigidae is shown to be a polyphyletic assemblage nested within the Salpingoecidae. We elaborate on a revised taxonomy that divides Choanoflagellatea into two orders: Craspedida and Acanthoecida. Craspedida is composed of species that possess an organic cell coating and contains the single family Salpingoecidae. Members of the predominantly marine Acanthoecida produce a siliceous lorica in addition to an organic coat and are contained in two families-the Acanthoecidae and Stephanoecidae fam. n. Previous studies of choanoflagellates have been hindered by cases of taxon misidentification as well as the limited resolution of 18S small subunit (SSU) rDNA phylogenies. Unfortunately, cases of misidentification have been heavily repeated in the literature. In an attempt to avoid further confusion, we highlight known instances of misnamed taxa. We also examine the suitability of SSU rDNA sequences alone for choanoflagellate phylogenetics and recommend the use of protein-coding genes, such as hsp90 and tubA, whenever possible. [ABSTRACT FROM AUTHOR]

The placement of Diopsina in a monophyletic clade with Diopsis and Eurydiopsis is confirmed and a sister group relationship between Diopsina and Diopsis recovered with moderate support. The clarification of the phylogenetic position of Diopsina nested deeply within Diopsini is of crucial importance for the understanding of the relationships and the evolution of various morphological characters within the family. [ABSTRACT FROM AUTHOR]

We conduct the first molecular studies of the higher level phylogeny of bethylid wasps (Hymenoptera: Bethylidae). Sequences of the 500-bp D2/D3 expansion regions of the nuclear 28S rRNA gene are obtained for 33 bethylid species in 18 genera covering all four commonly recognized subfamilies, and an additional 13 outgroup species. A 450-bp sequence of the mitochondrial 16S rRNA gene is obtained for a smaller subset of those species. Strong support is found for the monophyly of Bethylidae, and for Bethylinae as the sister to the other bethylid subfamilies. Pristocerinae are supported as monophyletic. A species of Mesitiinae clusters with the Sclerodermini (sensu lato), these two strongly supported as a monophyletic clade. The Epyrini are supported as monophyletic, but our data do not demonstrate whether Pristocerinae or the Mesitiinae+Sclerodermini clade are their closest relatives. Kishino–Hasegawa tests reject the monophyly of the Epyrinae. Our results are consistent with Kieffer's original five major subtaxa of Bethylidae. [ABSTRACT FROM AUTHOR]

The choanoflagellates are a widespread group of heterotrophic aquatic nanoflagellates, which have recently been confirmed as the sister-group to Metazoa. Asexual reproduction is the only mode of cell division that has been observed within the group; at present the range of reproductive modes, as well as the ploidy level, within choanoflagellates are unknown. The recent discovery of long terminal repeat retrotransposons within the genome of Monosiga brevicollis suggests that this species also has sexual stages in its life cycle because asexual organisms cannot tolerate retrotransposons due to the rapid accumulation of deleterious mutations caused by their transposition. We screened the M. brevicollis genome for known eukaryotic meiotic genes, using a recently established “meiosis detection toolkit” of 19 genes. Eighteen of these genes were identified, none of which appears to be a pseudogene. Four of the genes were also identified in expressed sequence tag data from the distantly related Monosiga ovata. The presence of these meiosis-specific genes provides evidence for meiosis, and by implication sex, within this important group of protists. [ABSTRACT FROM AUTHOR]

The choanoflagellates are a ubiquitous group of nanoflagellates and the sister group of Metazoa. Examination of the initial draft version of the first choanoflagellate genome, that of Monosiga brevicollis, reveals the presence of three novel families of long terminal repeat (LTR) retrotransposons and an apparent absence of non-LTR retrotransposons and transposons. One of the newly discovered LTR families falls in the chromovirus clade of the Ty3/gypsy group while the other two families are closely related members of the Ty1/copia group. Examination of EST sequences and nucleotide analyses show that all three families are transcriptionally active and potentially functional within the genome of M. brevicollis. [Copyright &y& Elsevier]

Abstract: A new genus, Helgoeca gen. nov., has been designated to accommodate a nudiform loricate choanoflagellate (American Type Culture Collection strain ATCC 50073) that was incorrectly attributed to the tectiform genus Acanthoecopsis (=Acanthocorbis). The first indication that this species might be nudiform came from a four-gene phylogeny of the choanoflagellates which recovered ATCC 50073 within a strongly supported monophyletic clade comprising two other nudiform taxa. Fortunately an isolate of the species in question was available from the ATCC and when observed in rapidly growing culture it was immediately apparent that this species divided with the production of ‘naked’ motile cells; a typically nudiform character. The beaker-shaped lorica of this species consists of an outer layer of approximately 11 longitudinal costae, which terminate anteriorly as spines, and an equal or larger number of helical costae, with a left-handed conformation, each of which terminates anteriorly adjacent to the base of a spine. The pattern of costae in this species is indistinguishable from that of Acanthocorbis nana Thomsen and for this reason A. nana has been transferred to the new genus Helgoeca gen. nov., as the type species. [Copyright &y& Elsevier]

Background: In stalk-eyed flies (Diopsidae) the eyes and antennae are laterally displaced at the ends of elongated eyestalks. Eyespan and the degree of sexual dimorphism in eyespan vary considerably between species and several sexually dimorphic species show sexual selection through female mate preference for males with exaggerated eyespan. The genes on which selection acts to regulate eyespan remain to be identified. This could be achieved by comparing gene expression during eyestalk development in males and females if the sex of pre-adult flies could be reliably assigned. Here we describe two techniques, one morphological and one microsatellitebased, that identify the sex of stalk-eyed fly larvae and pupae. Results: We showed that genital discs of the stalk- yed fly Teleopsis dalmanni have two highly distinct morphologies, compact ("C") and lobed ("L"). Segment composition (revealed by Engrailed expression) was consistent with C morphology being typical of males and L morphology of females. We confirmed the proposed association between disc morphology and sex by evaluating the combined heterozygosity of four X-linked microsatellite markers. We demonstrated that individuals with C genital discs had hemizygous (male) genotypes while those with L discs were heterozygous (female) genotypes. Similar dimorphism in genital disc morphology was observed in eight other species spanning three representative Diopsid genera. In every case the segment composition supported C morphology being male and L morphology female. We assigned larval sex by C or L morphology and compared cell division frequencies in male and female eye-antennal discs in two species (T. dalmanni and Diasemopsis meigenii) sexually dimorphic for eyespan. The number of mitotic (anti-H3- abelled) cells did not differ between the sexes in either species. Conclusion: We have made novel use of two complementary techniques for identifying the sex of pre-adult stalk- yed flies. These procedures will facilitate studies of the evolution of sexually dimorphic development in a variety of other species. Morphology and En expression in male and female genital discs are highly conserved within each genus of Diopsidae. Finally, sexual dimorphism for eyespan in two Diopsid species is unlikely to be due to an increased rate of cell division at the third larval instar in males. [ABSTRACT FROM AUTHOR]

The article summarizes a study that sought to investigate the patterns of use and provision of online information by churches, by means of a case study of the Diocese of Southwark in the Church of England. In the United States, a quarter of all Internet users use it to find religious material, and the dissemination of religious material provided via the Internet is huge. Within Christianity alone many Internet ministries exist, and just as religion was a pioneering force in making use of printing press, so religions have been eager to spread their messages via the medium of the World Wide Web. After pornography and medicine, religion is the third most popular topic on the Web. The Anglican Church has a strong Internet presence too. The Church of England and most of its dioceses have web sites, and amongst the sections of the Church of England web site is information about the Anglican church and its faith. A more systematic approach to providing information online has been attempted through "The Anglican Domain," which links into the Anglican Church throughout the world.

There has been debate over the mechanisms that control the copy number of transposable elements in the genome of Drosophila melanogaster. Target sites in D. melanogaster populations are occupied at low frequencies, suggesting that there is some form of selection acting against transposable elements. Three main theories have been proposed to explain how selection acts against transposable elements: insertions of a copy of a transposable element are selected against; chromosomal rearrangements caused by ectopic exchange between element copies are selected against; or the process of transposition itself is selected against. The three theories give different predictions for the pattern of transposable element insertions in the chromosomes of D. melanogaster. We analysed the abundance of six LTR (long terminal repeat) retrotransposons on the X and fourth chromosomes of multiple strains of D. melanogaster, which we compare with the predictions of each theory. The data suggest that no one theory can account for the insertion patterns of all six retrotransposons. Comparing our results with earlier work using these transposable element families, we find a significant correlation between studies in the particular model of copy number regulation supported by the proportion of elements on the X for the different transposable element families. This suggests that different retrotransposon families are regulated by different mechanisms. [ABSTRACT FROM AUTHOR]

The fourth chromosome of Drosophila melanogaster lacks meiotic recombination. There is also a lack of nucleotide variation on the chromosome. This lack of variation could have been caused by a recent selective sweep, by background selection, or by a combination of these two forces. It should be possible to differentiate between the two mechanisms by studying the frequencies of polymorphic sites on the chromosome: a selective sweep should have resulted in low-frequency polymorphisms, whereas higher frequency polymorphisms would indicate the action of background selection. We have analyzed retrotransposable element insertions on the fourth chromosome in 11 strains of D. melanogaster. The polymorphisms found have a range of frequencies, with the presence of some insertions with high frequencies suggesting that the lack of variation is the result of background selection. We summarize the data using two statistics: the number of sites shared by more than one of the sample of 11 chromosomes (internal sites) and the mean number of transposable element differences in presence or absence between the sampled chromosomes. Simulations indicate that a selective sweep occurring more than 15,000 (0.03N) generations ago cannot be ruled out from the number of internal sites, although the number of differences between the chromosomes suggests either background selection or a sweep occurring more than 60,000 (0.12N) generations ago. Our results show no homoplasies and are thus consistent with no recombination occurring on the chromosome. The difficulties of distinguishing between the models using polymorphism data are discussed. [ABSTRACT FROM PUBLISHER]

An alcoholic with no history of clinical pancreatitis was found to have pancreas divisum and marked changes of chronic pancreatitis isolated to the ventral pancreas. Pancreas divisum has been suggested to cause recurrent pancreatitis in some patients. Gross and histologic changes of pancreatitis in only the dorsal pancreas of surgically resected specimens from patients with pancreas divisum is thought to support the concept that obstruction at the minor papilla produces dorsal pancreatitis. Alternative explanations for the occurrence of segmental pancreatitis and the possible synergistic role of ethanol and bile are reviewed. [ABSTRACT FROM AUTHOR]

The evidence for variations in winter phosphate concentration as a component of the ‘Russell Cycle’ has been re-examined. The change from high phosphate concentrations prior to 1930 is the largest apparent variation in concentration through the period 1923–1987. However, these values are the result of a retrospective application in 1938, of a salt correction factor of 1–35. The justification for this factor is examined. It is concluded that there is sufficient uncertainty in the accuracy of the pre-1948 measurements of phosphate concentration to preclude their use in long time-series analysis. A statistical analysis of the post-1948 data shows that a simple first order autoregression model provides a perfectly adequate description of the data; the data can be considered as essentially random, with a small component of carry over from one year to the next. The evidence is weak that variations in winter concentrations of phosphate support the Russell Cycle hypothesis. [ABSTRACT FROM PUBLISHER]