The extent of linkage disequilibrium in Arabidopsis thaliana.

Linkage disequilibrium (LD), the nonrandom occurrence of alleles in haplotypes, has long been of interest to population geneticists. Recently, the rapidly increasing availability of genomic polymorphism data has fueled interest in LD as a tool for fine-scale mapping, in particular for human disease loci. The chromosomal extent of LD is crucial in this context, because it determines how dense a map must be for associations to be detected and, conversely, limits how finely loci may be mapped. Arabidopsis thaliana is expected to harbor unusually extensive LD because of its high degree of selfing. Several polymorphism studies have found very strong LD within individual loci, but also evidence of some recombination. Here we investigate the pattern of LD on a genomic scale and show that in global samples, LD decays within approximately 1 cM, or 250 kb. We also show that LD in local populations may be much stronger than that of global populations, presumably as a result of founder events. The combination of a relatively high level of polymorphism and extensive haplotype structure bodes well for developing a genome-wide LD map in A. thaliana.     

Phorbol ester and Epstein-Barr virus dependent transformation of normal primary human skin epithelial cells

Substantial evidence has implicated Epstein-Barr virus (EBV) in the aetiology of two human neoplasms, nasopharyngeal carcinoma (NPC) and Burkitt's lymphoma. This is supported by the presence of high antibody titres to EBV early antigen and virus capsid antigen, as well as antibody to two viral-associated enzymes, DNase and DNA polymerase. Patients with NPC, particularly the undifferentiated form, are commonly found to have EBV DNA in the tumour. Ito and others have presented strong epidemiological evidence that phorbol esters are related to the unusual geographic distribution of NPC in southeastern regions of China. There appears to be a close link between the widespread EBV infection of the Asian population and the distinct regional distribution in China of plants that produce diterpene ester. Naturally occurring phorbol esters are produced by plants of the Euphorbiaceae and Thymelaeaceae, which are used as traditional herbal medicines. Although it has been established that EBV can infect epithelial cells isolated from NPC as well as certain normal epithelial cells, there has been no in vitro evidence that EBV induces neoplastic transformation in normal human epithelial cells with or without exposure to phorbol esters. We report here evidence that transformation of normal human epithelial cells results from exposure to infectious EBV and that transformation is dependent on the presence of phorbol esters.     

The species of Astymachus Howard (Hymenoptera: Encyrtidae), potentially important parasitoids of Aclerdidae (Hemiptera: Coccoidea) associated with grasses (Poaceae), with descriptions of three new species

ABSTRACT

Species of Astymachus (Hymenoptera: Encyrtidae) are of potential economic importance as primary parasitoids of aclerdids (Hemiptera: Aclerdidae) on grasses (Poaceae). We review the known species and describe three as new, bringing the total to eight. The species are characterised by means of a dichotomous key, diagnoses and illustrations and their known hosts are summarised.

http://www.zoobank.org/urn:lsid:zoobank.org:pub:324E4AF7-3032-4573-98AC-CABAE316F33E