Showing papers by "Mark Wilkinson published in 2001"

Age-dependent transformation frequency in elite wheat varieties

Abstract: Wheat is a major world crop and as such is a primary target for improvement of agronomic characteristics via genetic engineering. Optimization of transformation is essential in order to overcome the relatively low transformation frequencies encountered with wheat. Transformation of elite wheat varieties is not always successful due to variability in regeneration and transformation frequencies between varieties. In this work, two elite wheat varieties with a relatively high embryogenic capacity were transformed by particle bombardment. A strong correlation between transformation frequency and the age of wheat donor plants was observed in both varieties. The mean transformation frequency rose from 0.7% to 5% when using immature embryos from old and young donor plants, respectively. This was observed in both varieties, the best bombardments achieving up to 7.3% frequency. Using explants at an optimal developmental stage from donor plants grown under environmentally-controlled conditions has improved the reproducibility of transformation efficiency of elite wheat varieties and leads to the production of apparently phenotypically normal, fertile, transgenic plants.

Permanent marking of a fossorial caecilian, Gegeneophis ramaswamii (Amphibia: Gymnophiona: Caeciliidae)

Abstract: Despite the importance of permanent marking of animals for quantitative ecological studies, no such technique has been applied to any of the poorlyknown caecilian amphibians. We evaluated four techniques (Panjet, freezebranding, Elastomer Visible Implant tags and Soft Visible Implant Alphanumeric tags) of permanently marking a fossorial caecilian, Gegeneophis ramaswamii Taylor, in the southern Western Ghats, India. All the tested techniques are viable options for marking caecilians in the field but differ in their portability, ease and speed of application, and their suitability for batch and/or individual marking of animals. Panjet tattoos were deemed to be particularly effective and practical for batch marking, while Soft Visible Implant Alphanumeric tags offer good potential for individual marking.

Rheumatology: 14. Diagnosis and management of anterior knee pain

Abstract: The case A 32-year-old male runner visits his family physician in late spring complaining of pain in his knees over the past month. The pain is mostly anterior but is not well localized. It is aggravated by running, especially on hills, but subsides after the patient stops running. The patient has

The imbalance of paleontological trees

Abstract: One of the most extensively studied aspects of phylogenetic tree shape is balance, which is the extent to which nodes divide a tree into clades of equal size. Several authors have stressed the importance of tree balance for understanding patterns of evolution. It has been remarked that paleontological studies commonly produce very unbalanced trees (also called pectinate cladograms or “Hennigian combs”). This claim is tested here by comparing the balance of 50 paleontological trees and 50 neontological trees, all taken from the recent literature. Each tree was reanalyzed from the published data matrix to ensure its accuracy. The results confirm that paleontological trees tend to be more imbalanced than neontological trees. That paleontological trees are more imbalanced has been represented as a shortcoming of fossil data sets, but here it is argued that this is the expected result. Even under a simple Markovian model in which all speciations and extinctions occur randomly and with equal probability in all parts of the tree, trees based on taxa from a single time period (e.g., the present day) are generally more balanced than trees based on all taxa that ever existed within the clade. Computer simulation is used to calculate the expected balance and standard deviation of trees for up to 40 terminal taxa over the entire history of a model clade. The balance is measured using Colless's index, Ic, and the expected balance conforms well with published paleontological trees. The study underlines the difficulty of applying neontological tree statistics in paleontology.

Efficiency of strict consensus trees.

Abstract: Consensus trees are used in phylogenetics as summaries or representations of sets of source trees. Here we ask ‘How good are consensus trees?’ in the sense of how well do individual consensus trees represent the set of source trees for which they stand? There are many different consensus methods and various contexts in which they may be used (Swofford, 1991; Wilkinson, 1994; Leclerc, 1998). Consequently, answers to our question must be speciŽc as to both method and context. For example, majority-rule consensus trees (Margush and McMorris, 1981; Wilkinson, 1996) can provide useful graphical summaries of bootstrap or jackknife analyses but can be problematic when used to represent a set of equally optimal trees from the analysis of a single data set (Wilkinson and Benton, 1996). Here we focus on strict consensus methods sensu Wilkinson (1994), that is, methods that require unanimous agreement among the source trees, and on the contexts in which they are commonly used. Contexts in which strict consensus methods are used include the representation of the set of optimal trees for a single data set, the comparison of simulated trees and trees inferred from simulated data, and the quantiŽcation of the similarity of trees derived from different data sets in studies of taxonomic congruence. Here we describe a simple measure of consensus efŽciency that allows us to say how well a particular strict consensus tree is doing its job of faithfully representing the source trees. Consensus methods differ in the type of information they represent and the level of agreement required among the source trees for information of that type to be included in the consensus tree (Page, 1992). This is reected in the consensus terminology of Wilkinson (1994), as we use here, in which the names of consensus methods combine descriptors of the type of information (e.g., component, Adams) and the level of agreement (e.g., strict, majority-rule). Strict consensus trees provide information by permitting (or, conversely, prohibiting) a subset of the possible trees (Page, 1992; Wilkinson, 1994; Thorley et al., 1998). Consensus efŽciency is a relation between the trees permitted by the consensus tree and the source trees. An ideal or maximally efŽcient strict consensus tree would permit only the source trees that it represents. Consensus trees might deviate from the ideal in two ways. First, they might permit trees that are not source trees, and second they might fail to permit some of the source trees. Both behaviors would reduce the correspondence between the consensus and the source trees the consensus is intended to represent and thereby would reduce the efŽciency of the consensus tree. In practice, strict consensus trees must permit all the source trees. Thus the efŽciency of consensus trees is maximal when it permits only the source trees and is reduced as it permits additional trees. A maximally inefŽcient consensus representation is a consensus tree that prohibits no trees (i.e., a bush) when the set of source trees does not include all possible binary trees. A measure of consensus efŽciency (CE) that has these properties and that ranges between values of zero (minimal efŽciency) and one (maximal efŽciency) is given by:

Transformation of elite wheat varieties for improved end-use qualities: modification of gibberellin levels and pre-harvest sprouting

Abstract: Wheat was the last of the agriculturally important cereals to be transformed. The ability to introduce genes into wheat remains a technically demanding and relatively inefficient process, mainly confined to culture-responsive but commercially irrelevant genotypes such as Bobwhite. IACR-Rothamsted has developed robust transformation protocols, and in recent years, produced over four hundred independently transformed wheat lines in a wide range of commercial varieties, including Imp, Buster and Rialto. In this paper we summarise our wheat transformation protocols and describe our initial findings from two transformation projects that investigate the role of key proteins in regulating gibberellin biosynthesis and dormancy which have potential to improve end-use quality of bread wheat by reducing pre-harvest sprouting (PHS).