We previously proposed a "counting model" for meiotic crossover interference, in which double-strand breaks occur independently and a fixed number of noncrossovers occur between neighboring crossovers. Whereas in some organisms (group I) this simple model alone describes the crossover distribution, in other organisms (group II) an additional assumption-that some crossovers lack interference-improves the fit. Other differences exist between the groups: Group II needs double-strand breaks and some repair functions to achieve synapsis, while repair in group I generally occurs after synapsis is achieved; group II, but not group I, has recombination proteins Dmc1, Mnd1, and Hop2. Here we report experiments in msh4 mutants that are designed to test predictions of the revised model in a group II organism. Further, we interpret these experiments, the above-mentioned differences between group I and II meiosis, and other data to yield the following proposal: Group II organisms use the repair of leptotene breaks to promote synapsis by generating double-Holliday-junction intermediates that lock homologs together (pairing pathway). The possible crossover or noncrossover resolution products of these structures lack interference. In contrast, for both group I and group II, repair during pachytene (disjunction pathway) is associated with interference and generates only two resolution types, whose structures suggest that the Holliday junctions of the repair intermediates are unligated. A crossover arises when such an intermediate is stabilized by a protein that prevents its default resolution to a noncrossover. The protein-binding pattern required for interference depends on clustering of sites that have received, or are normally about to receive, meiotic double-strand breaks.A key feature of meiosis in most organisms is crossing map) and still beguiles geneticists, microscopists, and mathematicians alike. over, the process in which homologous chromosomes exchange segments during the repair of programmed A mathematical model that effectively describes linkage data from the X chromosome of Drosophila (McPeek and double-strand breaks (DSBs) in their DNA. The frequencies of crossing over provide the basis for genetic Speed 1995; Zhao et al. 1995) was put forth by Cobbs (1978) and Stam (1979). Their model, notable for its linkage mapping (Sturtevant 1913), in which the dissimplicity and mathematical tractability, was foreshadtance between genes (in morgans) is defined as the owed by several others (reviewed in Bailey 1961). It average number of points of crossing over in the interval describes the probability distribution for the linkage that separates the genes (Haldane 1919). Sturtevant distances (in morgans) between adjacent crossovers as (1915) and Muller (1916) noted that crossovers occura scaled chi-square probability distribution with an even ring during Drosophila melanogaster oogenesis show a kind number of degrees of freedom. Such a distribution of territoriality-a relatively equitable, nonrandom disgained biolog...

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One of the most important principles of scientific endeavour is that the results be reproducible from lab to lab. Although research groups rarely redo the published experiments of their colleagues, research plans almost always rely on the work of someone else. The assumption is that if the same experiment were repeated in another lab, results would be so similar that the same interpretation would be favoured. This notion allows one researcher to compare his/her own results to earlier work from other labs. An essential prerequisite for this is that the experiments are done in identical conditions and therefore the methodology must be clearly stated. While this may be scientific common sense, adherence is difficult because "standard" methods vary from one laboratory to another in subtle ways that are often not reported. More importantly, for many years the field ofyeast meiotic recombination considered typical differences to be innocuous. This chapter will highlight the documented environmental and genetic variables that are known to influence meiotic recombination in Saccharomyces cerevisiae. Other potential methodological sources of variation in meiotic experiments are also discussed. A careful assessment of the effects of these variables, has led to insights into our understanding of the control of recombination and meiosis.

Manure compost is a unique microenvironment which harbours potential new microorganisms that is able to produce a variety of anti-infective agents. However, the exploration of this ecosystem for actinomycetes and its bioactive secondary metabolites remained understudied. Therefore, this study aims to study the diversity of manure compost actinomycetes and to investigate their antimicrobial potential using conventional disc diffusion method and a modified resazurin microtiter based approach. A collection of 191 actinomycete isolates were recovered from 5 types of manure composts collected around Selangor, Malaysia. Utilizing a combination of micromorphological characteristics and 16S rRNA sequence analysis, the isolated actinomycetes were grouped into 12 genera within 9 families. Streptomyces spp. dominated the culture collection (79.1%) while the rest belonged to the non-Streptomyces group (20.9%), including an unusual isolate from the genus Verrucosispora. The evaluation of antimicrobial activities demonstrated that 21.5% of the isolates exhibited antagonistic effect against at least one of the test microorganisms with strong inhibition observed against fungal strains compared to pathogenic bacteria. A modified resazurin microtiter based assay was also developed and displayed higher sensitivity (40.0%) compared to the disc diffusion assay (26.0%). All ten actinomycete isolates which displayed narrow and broad spectrum effects also produce pigmented extracts. The results demonstrated that manure compost actinomycetes could be a promising source of novel bioactive agents and that the resazurin microtiter based assay is a more sensitive approach in screening antimicrobial properties of large numbers of microbial extracts.

Bioactive compounds that exhibit antimicrobial properties in frogs are parts of the animal defense against microbial infections.  The lyophilized frog’s skin secretions containing varies bioactive compounds were subjected to screen for their antimicrobial activity. This study was conducted as part of an effort on the search of antimicrobial peptides (AMPs) profiles of Malaysian frogs. The results indicate the collected frog skin secretion has antimicrobial effect against Gram-negative and Gram-positive bacteria.  BLAST and standard phylogenetics were used to establish a preliminary identity of the frog samples.