RESUMO
Recently, the Single-Cut-or-Join (SCJ) operation was proposed as a basis for a new rearrangement distance between multichromosomal genomes, leading to very fast algorithms, both in theory and in practice. However, it was not clear how well this new distance fares when it comes to using it to solve relevant problems, such as the reconstruction of evolutionary history. In this paper, we advance current knowledge, by testing SCJ's ability regarding evolutionary reconstruction in two aspects: 1) How well does SCJ reconstruct evolutionary topologies? and 2) How well does SCJ reconstruct ancestral genomes? In the process of answering these questions, we implemented SCJ-based methods, and made them available to the community. We ran experiments using as many as 200 genomes, with as many as 3,000 genes. For the first question, we found out that SCJ can recover typically between 60 percent and more than 95 percent of the topology, as measured through the Robinson-Foulds distance (a.k.a. split distance) between trees. In other words, 60 percent to more than 95 percent of the original splits are also present in the reconstructed tree. For the second question, given a topology, SCJ's ability to reconstruct ancestral genomes depends on how far from the leaves the ancestral is. For nodes close to the leaves, about 85 percent of the gene adjacencies can be recovered. This percentage decreases as we move up the tree, but, even at the root, about 50 percent of the adjacencies are recovered, for as many as 64 leaves. Our findings corroborate the fact that SCJ leads to very conservative genome reconstructions, yielding very few false-positive gene adjacencies in the ancestrals, at the expense of a relatively larger amount of false negatives. In addition, experiments with real data from the Campanulaceae and Protostomes groups show that SCJ reconstructs topologies of quality comparable to the accepted trees of the species involved. As far as time is concerned, the methods we implemented can find a topology for 64 genomes with 2,000 genes each in about 10.7 minutes, and reconstruct the ancestral genomes in a 64-leaf tree in about 3 seconds, both on a typical desktop computer. It should be noted that our code is written in Java and we made no significant effort to optimize it.
Assuntos
Rearranjo Gênico , Genômica/métodos , Modelos Genéticos , Filogenia , Animais , Campanulaceae , Simulação por Computador , Evolução Molecular , Genoma , SoftwareRESUMO
Cattle are divided into 2 groups referred to as taurine and indicine, both of which have been under strong artificial selection due to their importance for human nutrition. A side effect of this domestication includes a loss of genetic diversity within each specialized breed. Recently, the first taurine genome was sequenced and assembled, allowing for a better understanding of this ruminant species. However, genetic information from indicine breeds has been limited. Here, we present the first genome sequence of an indicine breed (Nellore) generated with 52X coverage by SOLiD sequencing platform. As expected, both genomes share high similarity at the nucleotide level for all autosomes and the X chromosome. Regarding the Y chromosome, the homology was considerably lower, most likely due to uncompleted assembly of the taurine Y chromosome. We were also able to cover 97% of the annotated taurine protein-coding genes.
Assuntos
Bovinos/genética , Genoma , Animais , Cromossomos de Mamíferos/genética , Códon/genética , Mapeamento de Sequências Contíguas , Masculino , Análise de Sequência de DNA , Homologia de Sequência do Ácido NucleicoRESUMO
The breakpoint distance is one of the most straightforward genome comparison measures. Surprisingly, when it comes to defining it precisely for multichromosomal genomes with both linear and circular chromosomes, there is more than one way to go about it. Pevzner and Tesler gave a definition in a 2003 paper, Tannier et al. defined it differently in 2008, and in this paper we provide yet another alternative, calling it SCJ for single-cut-or-join, in analogy to the popular double cut and join (DCJ) measure. We show that several genome rearrangement problems, such as median and halving, become easy for SCJ, and provide linear and higher polynomial time algorithms for them. For the multichromosomal linear genome median problem, this is the first polynomial time algorithm described, since for other distances this problem is NP-hard. In addition, we show that small parsimony under SCJ is also easy, and can be solved by a variant of Fitch's algorithm. In contrast, big parsimony is NP-hard under SCJ. This new distance measure may be of value as a speedily computable, first approximation to distances based on more realistic rearrangement models.
Assuntos
Algoritmos , Rearranjo Gênico/genética , Genômica/métodos , Modelos Genéticos , FilogeniaRESUMO
We present the first two mitochondrial genomes of Muscidae dipterans for the species Haematobia irritans (the horn fly) and Stomoxys calcitrans (the stable fly). Typical insect mtDNA features are described, such as a high A+T content (79.1% and 78.9%, respectively), the preference for A+T-rich codons, and the evidence of a non-optimal codon usage. The strong A+T enrichment partially masks another nucleotide content bias maintained by A+C mutation pressure in these Muscidae mtDNAs. The analysis of this data provides a model of metazoans tRNA anticodon evolution, based on the selection hypothesis of anticodon versatility. H. irritans mitochondrial genome (16078 bp) is structurally similar to the hypothetical ancestral mitochondrial genome of arthropods and its control region (A+ T-rich region in insects) organization is consistent with the structure described for Brachycera dipterans. On the other hand, the mitochondrial genome of S. calcitrans is approximately 2kb longer (18 kb), characterized by the presence of approximately 550 bp tandem repeats in the control region, and an extra copy of trnI remarkably similar to a duplicated element of blowflies mtDNA. Putative sequence elements, involved in the regulation of transcription and replication of the mtDNA, were reliably identified in S. calcitrans control region despite the 0.8-1.5 kb gap uncovered from this genome. The use of amino acid and nucleotide sequences of concatenated mitochondrial protein-coding genes (PCGs) in phylogenetic reconstructions of Diptera does not support the monophyly of Muscomorpha, as well as the monophyly of Acalyptratae. Within the Calyptratae group, the inclusion of Muscidae (Muscoidea) as a sister group of Calliphoridae (Oestroidea) implies in a potential conflict concerning the monophyly of the superfamily Oestroidea.
Assuntos
DNA Mitocondrial/genética , Genoma Mitocondrial , Muscidae/genética , Animais , Evolução Biológica , Códon , Duplicação Gênica , Genes de Insetos , Genes Mitocondriais , Variação Genética , Genoma , Modelos Genéticos , Filogenia , RNA de Transferência/metabolismo , Transcrição GênicaRESUMO
UNLABELLED: The Arthropodan Mitochondrial Genomes Accessible database (AMiGA) is a relational database developed to help in managing access to the increasing amount of data arising from developments in arthropodan mitochondrial genomics (136 mitochondrial genomes as of September 2005). The strengths of AMiGA include (1) a more accessible and up-to-date database containing a more comprehensive set of mitochondrial genomes for this phylum, (2) the provision of flexible search options for retrieving detailed information such as bibliographical data, genomic graphics, FASTA sequences and taxonomical status, (3) the possibility of enhanced comparative analyses by multiple alignment of single or concatenated sets of genes, (4) more accurate and updated information resulting from a specific curation process called AMiGA Notes and (5) the possibility of including unpublished sequences in a password-restricted area for comparative analysis with the other sequences stored in the database. AVAILABILITY: http://amiga.cbmeg.unicamp.br CONTACT: lessinger@amiga.cbmeg.unicamp.br SUPPLEMENTARY INFORMATION: Detailed information, including an illustrated tutorial, is available from the above URL.