Biomedical subjects

Michael D Bennett

Publications and source records attributed to Michael D Bennett.

8 recordsLinked to original sources

PubMed2007

Correlated evolution of genome size and seed mass.

Previous investigators have identified strong positive relationships between genome size and seed mass within species, and across species from the same genus and family. Here, we make the first broad-scale quantification of this relationship, using data for 1222 species, from 139 families and 48 orders. We analyzed the relationship between genome size and seed mass using a statistical framework that included four different tests. A quadratic relationship between genome size and seed mass appeared to be driven by the large genome/seed mass gymnosperms and the many small genome size/large seed mass angiosperms. Very small seeds were never associated with very large genomes, possibly indicating a developmental constraint. Independent contrast results showed that divergences in genome size were positively correlated with divergences in seed mass. Divergences in seed mass have been more closely correlated with divergences in genome size than with divergences in other morphological and ecological variables. Plant growth form is the only variable examined thus far that explains a greater proportion of variation in seed mass than does genome size.

Biological Evolution↗

PubMed2006

Pegaptanib for myopic choroidal neovascularization in a young patient.

BACKGROUND: The treatment of choroidal neovascularization (CNV) due to myopic degeneration can include laser photocoagulation, photodynamic therapy, corticosteroids, and subretinal surgery. We report a case of a young patient with myopic CNV refractive to laser photocoagulation, photodynamic therapy, and intravitreal triamcinolone acetonide treated with intravitreal pegaptanib injections. METHODS: Interventional case report. The medical chart of a 36-year-old female treated with intravitreal pegaptanib injections was reviewed for changes in visual acuity on the Early Treatment of Diabetic Retinopathy Study (ETDRS) chart, CNV leakage on fluorescein angiography, and adverse events reported. RESULTS: ETDRS visual acuity improved from counting fingers (CF) to 20/40 in the right eye after five, 6-weekly pegaptanib injections. CONCLUSIONS: This is the sentinel case of US Food and Drug Administration (FDA) approved pegaptanib usage for non-wet macular degeneration via an Investigational New Drug application (Title 21, Code of Federal Regulations part 132). Pegaptanib appears to be effective in treating myopic CNV refractive to laser photocoagulation, photodynamic therapy, and intravitreal triamcinolone acetonide.

Adult↗

PubMed2006

Eukaryotic genome size databases.

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.

Animals↗

PubMed2005

First nuclear DNA C-values for 18 eudicot families.

BACKGROUND AND AIMS: A key target set at the second Plant Genome Size Workshop, held at the Royal Botanic Gardens, Kew in 2003, was to produce first DNA C-value data for an additional 1 % of angiosperm species, and, within this, to achieve 75 % familial coverage overall (up from approx. 50 %) by 2009. The present study targeted eudicot families for which representation in 2003 (42.5 %) was much lower than monocot (72.8 %) and basal angiosperm (69.0 %) families. METHODS: Flow cytometry or Feulgen microdensitometry were used to estimate nuclear DNA C-values, and chromosome counts were obtained where possible. KEY RESULTS: First nuclear DNA C-values are reported for 20 angiosperm families, including 18 eudicots. This substantially increases familial representation to 55.2 % for angiosperms and 48.5 % for eudicots. CONCLUSIONS: The importance of targeting specific plant families to improve familial nuclear DNA C-value representation is reconfirmed. International collaboration will be increasingly essential to locate and obtain material of unsampled plant families, if the target set by the second Plant Genome Size Workshop is to be met.

Cell Nucleus↗

PubMed2005

The origin, evolution and proposed stabilization of the terms 'genome size' and 'C-value' to describe nuclear DNA contents.

BACKGROUND: Perusing the literature on nuclear 'genome size' shows that the term is not stabilized, but applied with different meanings. It is used for the DNA content of the complete chromosome complement (with chromosome number n), for which others use 'C-value', but also for the DNA content of the monoploid chromosome set only (with chromosome number x). Reconsideration of the terminology is required. AIM: Our purpose is to discuss the currently unstable usage of the terms 'genome size' and 'C-value', and to propose a new unified terminology which can describe nuclear DNA contents with ease and without ambiguity. PROPOSALS: We argue that there is a need to maintain the term genome size in a broad sense as a covering term, because it is widely understood, short and phonetically pleasing. Proposals are made for a unified and consensual terminology. In this, 'genome size' should mean the DNA content based on chromosome number x and n, and should be used mainly in a general sense. The necessary distinction of the kinds of genome sizes is made by the adjectives 'monoploid' and the neology 'holoploid'. 'Holoploid genome size' is a shortcut for the DNA content of the whole chromosome complement characteristic for the individual (and by generalization for the population, species, etc.) irrespective of the degree of generative polyploidy, aneuploidies, etc. This term was lacking in the terminology and is for reasons of linguistic consistency indispensable. The abbreviated terms for monoploid and holoploid genome size are, respectively, Cx-value and C-value. Quantitative data on genome size should always indicate the C-level by a numerical prefix, such as 1C, 1Cx, 2C, etc. The proposed conventions cover general fundamental aspects relating to genome size in plants and animals, but do not treat in detail cytogenetic particularities (e.g. haploids, hybrids, etc.) which will need minor extensions of the present scheme in a future paper.

Cell Nucleus↗

PubMed2003

First nuclear DNA C-values for 28 angiosperm genera.

This paper reports first DNA C-values for 28 angiosperm genera. These include first DNA C-values for 25 families, of which 16 are monocots. Overall familial representation is 47.2 % for angiosperms, but is now much higher for monocots (75 %) and basal angiosperms (73.1 %) than for eudicots (38.7 %). Chromosome counts are reported for 22 taxa, including first records for six genera plus seven species. Unrepresented families will become increasingly enriched for monotypic taxa from obscure locations that are harder to access. Thus, completing familial representation for genome size for angiosperms may prove impossible in any short period, and progress towards this goal will become slower.

Chromosomes, Plant↗

PubMed2003

Comparisons with Caenorhabditis (approximately 100 Mb) and Drosophila (approximately 175 Mb) using flow cytometry show genome size in Arabidopsis to be approximately 157 Mb and thus approximately 25% larger than the Arabidopsis genome initiative estimate of approximately 125 Mb.

Recent genome sequencing papers have given genome sizes of 180 Mb for Drosophila melanogaster Iso-1 and 125 Mb for Arabidopsis thaliana Columbia. The former agrees with early cytochemical estimates, but numerous cytometric estimates of around 170 Mb imply that a genome size of 125 Mb for arabidopsis is an underestimate. In this study, nuclei of species pairs were compared directly using flow cytometry. Co-run Columbia and Iso-1 female gave a 2C peak for arabidopsis only approx. 15 % below that for drosophila, and 16C endopolyploid Columbia nuclei had approx. 15 % more DNA than 2C chicken nuclei (with >2280 Mb). Caenorhabditis elegans Bristol N2 (genome size approx. 100 Mb) co-run with Columbia or Iso-1 gave a 2C peak for drosophila approx. 75 % above that for 2C C. elegans, and a 2C peak for arabidopsis approx. 57 % above that for C. elegans. This confirms that 1C in drosophila is approx. 175 Mb and, combined with other evidence, leads us to conclude that the genome size of arabidopsis is not approx. 125 Mb, but probably approx. 157 Mb. It is likely that the discrepancy represents extra repeated sequences in unsequenced gaps in heterochromatic regions. Complete sequencing of the arabidopsis genome until no gaps remain at telomeres, nucleolar organizing regions or centromeres is still needed to provide the first precise angiosperm C-value as a benchmark calibration standard for plant genomes, and to ensure that no genes have been missed in arabidopsis, especially in centromeric regions, which are clearly larger than once imagined.

Animals↗

PubMed2002

Nuclear DNA C-values in 30 species double the familial representation in pteridophytes.

Nuclear DNA C-values and genome size are important biodiversity characters with fundamental biological significance. Yet C-value data for pteridophytes, a diverse group of vascular plants with approx. 9000 extant species, remain scarce. A recent survey by Bennett and Leitch (2001, Annals of Botany 87: 335-345) found that C-values were reported for only 48 pteridophyte species. To improve phylogenetic representation in this group and to check previously reported estimates, C-values for 30 taxa in 17 families were measured using flow cytometry for all but one species. This technique proved generally applicable, but the ease with which C-value data were generated varied greatly between materials. Comparing the new data with those previously published revealed several large discrepancies. After discounting doubtful data, C-values for 62 pteridophyte species remained acceptable for analysis. The present work has increased the number of such species' C-values by 93 %, and more than doubled the number of families represented (from 10 to 21). Analysis shows that pteridophyte C-values vary approx. 450-fold, from 0-16 pg in Selaginella kraussiana to 72.7 pg in Psilotum nudum var. gasa. Superimposing C-value data onto a robust phylogeny of pteridophytes suggests some possible trends in C-value evolution and highlights areas for future work.

Cell Nucleus↗