Munch Lab


SAP – Statistical Assignment Package

The assignment of DNA from organic material to species or taxonomic groups is integral to a number of scientific disciplines. Metagenomics is an approach particularly suitable for viruses and bacterial species, which have a relatively small genome. The approach can be used to characterize environments according to their genetic fingerprint. Even without taking genomic approaches, however, DNA sequencing of selected markers from environmental samples may provide ecological information or identify relevant species such as human pathogens. A related field where unknown specimens are identified based on Cytochrome Oxidase I (COI) has become known as DNA Barcoding. The Statistical Assignment Package is a command line tool answer the central question in these fields: what taxonomic group does an unknown organism represented by a DNA sequence belong to? SAP uses a Bayesian approach to calculate a probability distribution over all taxa represented in a sequence database. The probability of assignment to each taxa serves as a measure of confidence in the assignment. SAP is available as a command line tool and as a web service.

Agene – Automatic generation of species-specific gene predictors

The number of sequenced eukaryotic genomes is rapidly increasing. This means that over time it will be hard to keep supplying customized gene finders for each genome. This calls for procedures to automatically generate species-specific gene finders and to re-train them as the quantity and quality of reliable gene annotation grows. We present a procedure, Agene, that automatically generates a species-specific gene predictor from a set of reliable mRNA sequences and a genome. We apply a Hidden Markov model (HMM) that implements explicit length distribution modeling for all gene structure blocks using acyclic discrete phase-type distributions. The state structure of the each HMM is generated dynamically from an array of sub-models to include only gene features represented in the training set. Acyclic discrete phase-type distributions are well suited to model sequence length distributions. The performance of each individual gene predictor on each individual genome is comparable to the best of the manually optimized species-specific gene finders. It is shown that species-specific gene finders are superior to gene finders trained on other species. The resulting gene finders can be accessed through the Agene server.

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