CiteULike: aprasad's Gregory

Genome size diversity in the family Drosophilidae

TR Gregory — 2008-06-04T15:45:33-00:00

Heredity, Vol. aop, No. current.

Flies in the genus Drosophila have been the dominant model organisms in genetics for over a century and, with a dozen complete sequences now available, continue as such in modern comparative genomics. Surprisingly, estimates of genome size for this genus have been relatively sparse, covering less than 2% of species. Here, best practice flow cytometric genome size estimates are reported for both male and female flies from 67 species from six genera in the family Drosophilidae, including 55 species from the genus Drosophila. Direct and phylogenetically corrected correlation analyses indicate that genome size is positively correlated with temperature-controlled duration of development in Drosophila, and there is indication that genome size may be positively related to body size and sperm length in this genus. These findings may provide some explanation for the streamlined genomes found in these insects, and complement recent work demonstrating possible selective constraints on further deletion of noncoding DNA.Heredity advance online publication, 4 June 2008; doi:10.1038/hdy.2008.49.

Population size and genome size in fishes: a closer look.

TR Gregory — 2008-05-12T18:03:32-00:00

Genome / National Research Council Canada = Génome / Conseil national de recherches Canada, Vol. 51, No. 4. (April 2008), pp. 309-313.

The several thousand-fold range in genome size among animals has remained a subject of active research and debate for more than half a century, but no satisfactory explanation has yet been provided. Many one-dimensional models have been postulated, but so far none has been successful in accounting for observed patterns in genome size diversity. The recent model based on differences in effective population size appeared to gain empirical support with a study of genome size and inferred effective population size in fishes, but there were several questionable aspects of the analysis. First, it was based on an assumption that microsatellite heterozygosity indicates long-term effective population size, whereas in actuality these markers evolve quickly and are sensitive to demographic events. Second, it included both ancient polyploids and non-polyploids, the former of which did not gain their current genome sizes through the accumulation of slightly deleterious mutations as required in the model. Third, the analysis neglected the tremendous influence that Pleistocene glaciation bottlenecks had on heterozygosities in freshwater (and far less so, marine) fishes. In sum, it is apparent that genomes reached their current sizes in most fishes long before contemporary microsatellite heterozygosities were shaped, and that ancient polyploidy rather than the accumulation of mildly deleterious transposon insertions in small populations is the dominant factor that has influenced the large end of the range of genome sizes among fishes.

Genome size, cell size, and the evolution of enucleated erythrocytes in attenuate salamanders.

Rachel Lockridge Mueller — 2008-05-09T17:02:00-00:00

Zoology (Jena, Germany), Vol. 111, No. 3. (1 May 2008), pp. 218-230.

Within the salamander family Plethodontidae, five different clades have evolved high levels of enucleated red blood cells, which are extremely unusual among non-mammalian vertebrates. In each of these five clades, the salamanders have large genomes and miniaturized or attenuated body forms. Such a correlation suggests that the loss of nuclei in red blood cells may be related, in part, to the interaction between large genome size and small body size, which has been shown to have profound morphological consequences for the nervous and visual systems in plethodontids. Previous work has demonstrated that variation in both the level of enucleated cells and the size of the nuclear genome exists among species of the monophyletic plethodontid genus Batrachoseps. Here, we report extensive intraspecific variation in levels of enucleated red blood cells in 15 species and provide measurements of red blood cell size, nucleus size, and genome size for 13 species of Batrachoseps. We present a new phylogenetic hypothesis for the genus based on 6150bp of mitochondrial DNA sequence data from nine exemplar taxa and use it to examine the relationship between genome size and enucleated red blood cell morphology in a phylogenetic framework. Our analyses demonstrate positive direct correlations between genome size, nucleus size, and both nucleated and enucleated cell sizes within Batrachoseps, although only the relationship between genome size and nucleus size is significant when phylogenetically independent contrasts are used. In light of our results and broader studies of comparative hematology, we propose that high levels of enucleated, variably sized red blood cells in Batrachoseps may have evolved in response to rheological problems associated with the circulation of large red blood cells containing large, bulky nuclei in an attenuate organism.

Insertion-deletion biases and the evolution of genome size.

TR Gregory — 2007-08-03T15:46:35-00:00

Gene, Vol. 324 (7 January 2004), pp. 15-34.

Numerous theories have been proposed to account for the pronounced differences in the quantity of non-coding DNA among eukaryotic genomes, but the current repertoire remains incomplete because the only explicit mechanisms it provides involve DNA gain. It has been proposed more recently that biases in spontaneous insertions and deletions (indels) can lead to genome shrinkage by mutational mechanisms alone. The present article provides the first detailed critical discussion of this approach, and covers three different ideas related to it: (1) the general notion of DNA loss by deletion bias, (2) the "DNA loss hypothesis" which supposes that variation in genome size can be attributed to differences in DNA loss rate, and (3) the "mutational equilibrium model" which attempts to describe the long-term evolution of genome size. The mutational equilibrium model is found to be problematic, and it is noted that DNA loss by small indels is too slow in real time to determine variation in genome size above a relatively low threshold. Some alternative explanations for the observed patterns are provided, and the critique also identifies some potential problems with the current dataset. These include a failure to cite a more detailed (and somewhat contradictory) mammalian dataset, a questionable use of arithmetic means with highly skewed data, and important discrepancies among the particular DNA sequences so far analyzed. Overall, evolutionary reductions in genome size are considered important, but the specific mechanism relating to small deletion bias is far too weak to be accepted as a primary determinant of genome size variation in general.

From pixels to picograms: a beginners' guide to genome quantification by Feulgen image analysis densitometry.

DC Hardie — 2007-08-03T15:04:39-00:00

J Histochem Cytochem, Vol. 50, No. 6. (June 2002), pp. 735-749.

The study of genome size variation is important from a number of practical and theoretical perspectives. For example, the long-standing "C-value enigma" relating to the more than 200,000-fold range in eukaryotic genome sizes is best studied from a broad comparative standpoint. Genome size data are also required in detailed analyses of genome structure and evolution. The choice of future genome sequencing projects will be dependent on knowledge regarding the sizes of genomes to be sequenced, and so on. To date, genome size data have been acquired primarily by Feulgen microdensitometry or flow cytometry. Each has several advantages but also important limitations. In this review, we provide a practical guide to the new technique of Feulgen image analysis densitometry. The review is designed for those interested in genome size measurements but not extensively experienced in histochemistry, densitometry, or microscopy. Therefore, relevant historical and technical background information is included. For easy reference, we provide recipes for required reagents, guidelines for cell staining, and a checklist of steps for successful image analysis. We hope that the accuracy, rapidity, and cost-effectiveness of Feulgen image analysis demonstrated here will stimulate further surveys of genome sizes in a variety of taxa.

Eukaryotic genome size databases.

T Ryan Gregory — 2006-11-13T20:33:17-00:00

Nucleic Acids Res (7 November 2006)

Three independent databases of eukaryotic genome size information have been launched or re-released in updated form since 2005: the Plant DNA C-values Database (www.kew.org/genomesize/homepage.html), the Animal Genome Size Database (www.genomesize.com) and the Fungal Genome Size Database (www.zbi.ee/fungal-genomesize/). In total, these databases provide freely accessible genome size data for >10 000 species of eukaryotes assembled from more than 50 years' worth of literature. Such data are of significant importance to the genomics and broader scientific community as fundamental features of genome structure, for genomics-based comparative biodiversity studies, and as direct estimators of the cost of complete sequencing programs.

Initial sequencing and comparative analysis of the mouse genome.

RH Waterston — 2004-11-22T00:17:30-00:00

Nature, Vol. 420, No. 6915. (5 December 2002), pp. 520-562.

The sequence of the mouse genome is a key informational tool for understanding the contents of the human genome and a key experimental tool for biomedical research. Here, we report the results of an international collaboration to produce a high-quality draft sequence of the mouse genome. We also present an initial comparative analysis of the mouse and human genomes, describing some of the insights that can be gleaned from the two sequences. We discuss topics including the analysis of the evolutionary forces shaping the size, structure and sequence of the genomes; the conservation of large-scale synteny across most of the genomes; the much lower extent of sequence orthology covering less than half of the genomes; the proportions of the genomes under selection; the number of protein-coding genes; the expansion of gene families related to reproduction and immunity; the evolution of proteins; and the identification of intraspecies polymorphism.

Synergy between sequence and size in Large-scale genomics

Ryan Gregory — 2005-09-01T17:01:41-00:00

Nature Reviews Genetics, Vol. 6, No. 9. (01 September 2005), pp. 699-708.

The Evolution of the Genome

Ryan Gregory — 2005-09-06T14:41:15-00:00

(22 December 2004)

The Evolution of the Genome provides a much needed overview of genomic study through clear, detailed, expert-authored discussions of the key areas in genome biology. This includes the evolution of genome size, genomic parasites, gene and ancient genome duplications, polypoidy, comparative genomics, and the implications of these genome-level phenomena for evolutionary theory. In addition to reviewing the current state of knowledge of these fields in an accessible way, the various chapters also provide historical and conceptual background information, highlight the ways in which the critical questions are actually being studied, indicate some important areas for future research, and build bridges across traditional professional and taxonomic boundaries. The Evolution of the Genome will serve as a critical resource for graduate students, postdoctoral fellows, and established scientists alike who are interested in the issue of genome evolution in the broadest sense. · Provides detailed, clearly written chapters authored by leading researchers in their respective fields · Presents a much-needed overview of the historical and theoretical context of the various areas of genomic study · Creates important links between topics in order to promote integration across subdisciplines, including descriptions of how each subject is actually studied · Provides information specifically designed to be accessible to established researchers, postdoctoral fellows, and graduate students alike