Lateral genomics

More than 20 complete prokaryotic genome sequences are now publicly available, each by itself an unparalleled resource for understanding organismal biology. Collectively, these data are even more powerful: they could force a dramatic reworking of the framework in which we understand biological evolution. It is possible that a single universal phylogenetic tree is not the best way to depict relationships between all living and extinct species. Instead a web- or net-like pattern, reflecting the importance of horizontal or lateral gene transfer between lineages of organisms, might provide a more appropriate visual metaphor. Here, I ask whether this way of thinking is really justified, and explore its implications.     

Lateral genomics

More than 20 complete prokaryotic genome sequences are now publicly available, each by itself an unparalleled resource for understanding organismal biology. Collectively, these data are even more powerful: they could force a dramatic reworking of the framework in which we understand biological evolution. It is possible that a single universal phylogenetic tree is not the best way to depict relationships between all living and extinct species. Instead a web- or net-like pattern, reflecting the importance of horizontal or lateral gene transfer between lineages of organisms, might provide a more appropriate visual metaphor. Here, I ask whether this way of thinking is really justified, and explore its implications.     

Lateral genomics

More than 20 complete prokaryotic genome sequences are now publicly available, each by itself an unparalleled resource for understanding organismal biology. Collectively, these data are even more powerful: they could force a dramatic reworking of the framework in which we understand biological evolution. It is possible that a single universal phylogenetic tree is not the best way to depict relationships between all living and extinct species. Instead a web- or net-like pattern, reflecting the importance of horizontal or lateral gene transfer between lineages of organisms, might provide a more appropriate visual metaphor. Here, I ask whether this way of thinking is really justified, and explore its implications.     

Lateral canthal anchoring

LEARNING OBJECTIVES: After studying this article, the participant should be able to: 1. Understand the principles involved in canthal support for patients undergoing cosmetic and reconstructive surgery. 2. Understand the variations in surgical techniques required to perform canthal anchoring in differing patients. 3. Describe the significance and techniques of canthal anchoring (canthoplasty and canthopexy) as they relate to cosmetic and reconstructive lower lid surgery. 4. Describe the effect of canthal anchoring on the function of the upper and lower lids and eyelid fissure shape. Any surgeon performing cosmetic or reconstructive surgery procedures on the lower lid or midface through the lower lid should be comfortable with canthal anchoring procedures. Appropriate canthal anchoring is effective in preventing postoperative lower-lid malposition, in ensuring eyelid closure, and in improving or maintaining proper eye shape. In many patients, a canthopexy (nonlysis canthal anchoring) is effective. However, in patients with significant horizontal laxity, cantholysis with appropriate lid shortening is required. It should be remembered that canthal anchoring, no matter how well performed, will not prevent severe lower-lid complications in cases of over-resection of lower-lid skin and of poorly performed midface procedures that do not support the lower lid and cheek.     

Anisophylly of Lateral Shoots

The inequality shown by anisophyllous leaves in plants withdecussate phyllotaxis can be measured as the difference in sizebetween the two leaves at a node, expressed as a percentageof their mean size. This is referred to as the degree of anisophylly. In Acer anisophylly of two types with different causation occurs.

1. 1. Primary anisophylly which is shown only by first year shootsdeveloped from axillary buds and which is due to the inequalityof the leaf primordia. Primary anisophylly is thus determinedby events occurring during the formation of the bud and is irreversible.
2. 2. Secondary amsophylly which is shown chiefly by the second(and subsequent) year's extension growth of lateral shoots frombuds which are isophyllous and which is due to the positionin which the shoot develops. This type of anisophylly is reversibleif the position of the developing shoot be changed.

Effects of secondary anisophylly may be superimposed on thoseof primary anisophylly. The recognition of these two causally distinct types of anisophyllyoccurring in one plant does much to resolve the apparently conflictinginformation available relating to lateral anisophylly.     

Lateral and oblique gene transfer

Sequence information from complete genomes, and from multiple loci of strains within species, is transforming the way that we investigate the evolution of bacteria. Such large-scale assessments of bacterial genomes have provided evidence of extensive gene transfer and exchange. Except in rare cases, these two processes do not seem to be coupled: certain species, such as Escherichia coli, undergo relatively low levels of gene exchange; but the emergence of pathogenic strains is associated with the acquisition of numerous virulence factors by lateral gene transfer.