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Rates of molecular evolution along phylogenetic trees are influenced by mutation, selection and genetic drift. Provided that the branches of the tree correspond to lineages belonging to genetically isolated populations (e.g., multi-species phylogenies), the interplay between these three processes can be described by analyzing the process of substitutions to the common ancestor of each population. We characterize this process for a class of diffusion models from population genetics theory using the structured coalescent process introduced by Kaplan et al. (1988) and formalized in Barton et al. (2004). For two-allele models, this approach allows both the stationary distribution of the type of the common ancestor and the generator of the common ancestor process to be determined by solving a one-dimensional boundary value problem. In the case of a Wright-Fisher diffusion with genic selection, this solution can be found in closed form, and we show that our results complement those obtained by Fearnhead (2002) using the ancestral selection graph. We also observe that approximations which neglect recurrent mutation can significantly underestimate the exact substitution rates when selection is strong. Furthermore, although we are unable to find closed-form expressions for models with frequency-dependent selection, we can still solve the corresponding boundary value problem numerically and then use this solution to calculate the substitution rates to the common ancestor. We illustrate this approach by studying the effect of dominance on the common ancestor process in a diploid population. Finally, we show that the theory can be formally extended to diffusion models with more than two genetic backgrounds, but that it leads to systems of singular partial differential equations which we have been unable to solve.

The African trypanosome Trypanosoma brucei is best known for its extraordinarily sophisticated antigenic variation of a protective variant surface glycoprotein (VSG) coat. T. brucei has >1000 VSG genes and pseudogenes, of which one is transcribed at a time from one of multiple telomeric VSG expression sites. Switching the active VSG gene can involve DNA rearrangements replacing the old VSG with a new one, or alternatively transcriptional control. The astonishing revelation from the T.bruceigenome sequence isthat

We report a case of a solitary infantile myofibroma masquerading as an ulcerated infantile hemangioma. Infantile myofibroma is a rare soft tissue tumor that has a good prognosis in the solitary form. It may be difficult to distinguish clinically from more common tumors of infancy such as an infantile hemangioma or from other rare entities and therefore requires a biopsy for definitive diagnosis.

Globally, human immunodeficiency virus–type 1 (HIV-1) is extraordinarily variable, and this diversity poses a major obstacle to AIDS vaccine development. Currently, candidate vaccines are derived from isolates, with the hope that they will be sufficiently cross-reactive to protect against circulating viruses. This may be overly optimistic, however, given that HIV-1 envelope proteins can differ in more than 30% of their amino acids. To contend with the diversity, country-specific vaccines are being considered, but evolutionary relationships may be more useful than regional considerations. Consensus or ancestor sequences could be used in vaccine design to minimize the genetic differences between vaccine strains and contemporary isolates, effectively reducing the extent of diversity by half.

Several empirical studies of sperm competition in populations polymorphic for a driving X chromosome have revealed that Sex-ratio males (those carrying a driving X) are at a disadvantage relative to Standard males. Because the frequency of the driving X chromosome determines the population-level sex ratio and thus alters male and female mating rates, the evolutionary consequences of sperm competition for sex chromosome meiotic drive are subtle. As the SR allele increases in frequency, the ratio of females to males also increases, causing an increase in the male mating rate and a decrease in the female mating rate. While the former change may exacerbate the disadvantage of Sex-ratio males during sperm competition, the latter change decreases the incidence of sperm competition within the population. We analyze a model of the effects of sperm competition on a driving X chromosome and show that these opposing trends in male and female mating rates can result in two coexisting locally stable equilibria, one corresponding to a balanced polymorphism of the SR and ST alleles and the second to fixation of the ST allele. Stochastic fluctuations of either the population sex ratio or the SR frequency can then drive the population away from the balanced polymorphism and into the basin of attraction for the second equilibrium, resulting in fixation of the SR allele and extinction of the population.

This chapter will discuss mechanisms of orbital trauma specific to the pediatric patient. It will identify differences in the effects of traumatic events to the orbital region between adults and young children, in particular. Current concepts in both evaluation and management, as they relate to the pediatric population, will be reviewed. The importance of early surgical intervention will be discussed as well as current techniques for managing the repair of orbital trauma in the pediatric patient.

Endoscopic laser photocoagulation is commonly used to treat bleeding from the neovascular lesions of chronic radiation proctopathy. The KTP laser is an Nd/YAG-driven unit that emits light with a wavelength of 532 nm. This wavelength of energy is absorbed by hemoglobin and penetrates tissue to a depth of only 1 to 2 mm.Twenty-three patients were treated with KTP laser and followed for a median of 29 months (range 5 to 51 months); 21 had received radiation for prostate cancer and 2 for uterine cancer. The median age was 77 years (range 68 to 87 years). A median of 2 sessions (range 1 to 5 sessions) was performed using 4 to 10 Watts of power and a median energy of 816 Joules per session (range 204 to 2430 Joules).After treatment there was a significant reduction in the frequency (p = 0.0005) of bleeding, increase in hematocrit level (p0.0001), improvement in activities of daily life (p = 0.01), and a reduction in use of health care resources (p0.0001). There was a trend toward decreased use of iron supplements (11 to 4 patients) and transfusions (4 to 0 patients). Two patients (9%) developed rectal ulcers after treatment.KTP laser photocoagulation is a safe and effective therapy for bleeding from chronic radiation proctopathy that improves activities of daily living and reduces use of health care resources.

Many types of scaffolds have been used in bone tissue engineering, with none emerging as favorites. We propose the use of acellular periosteum as a biologic scaffold to allow for progenitor cell adherence, migration, and proliferation in vitro and to test the construct in vivo in a rat calvarial defect model.Bovine periosteum was processed to remove all antigenic material (RTI Biologics), and its cambial layer was then seeded with adipose-derived stromal cells (ASCs) or periosteal-derived stromal cells (PSCs) and incubated for 14 days. Adherence required a fibronectin coat and was verified for both cell types via scanning electron microscopy and histology. Two 5-mm diameter calvarial defects were created in each of 19 rats. These were filled with xenograft bone chips and covered with acellular periosteum in combination with cells (ASC or PSC), growth factors (vascular endothelial growth factor, bone morphogenetic protein-2, or both), or alone (controls). Rats were killed 56 days postoperatively. Bone deposition was quantified by microcomputed tomography, and viability was determined histologically. Significance was determined through analysis of variance.Acellular allo-periosteum with a fibronectin coat permitted ASC and PSC adherence, migration, and proliferation in vitro. In the rat calvarial defects, the addition of stem cells (P.001) and growth factors (P.001) to the acellular periosteum increased de novo bone growth relative to controls. Although the stem cell source did not influence revitalization (P = .242), the combination of growth factors was more effective (P.001) than either growth factor alone. The interaction indicated that the 2 cell types did not respond equally to growth factors (P = .039).Acellular allo-periosteum is a biomimetic scaffold that permits pleuripotent cell adherence, migration, and proliferation in vitro. The combination of acellular periosteum, xenograft bone, stem cells, and growth factors may prove a viable combination for cranial bone tissue engineering.

In chronic radiation proctitis bleeding occurs from mucosal friability and neovascular telangiectasias. Fourteen patients with bleeding from chronic radiation proctitis underwent endoscopic argon laser therapy at 4 to 8 W. The goal of treatment was obliteration of all telangiectasias. The average follow-up was 35 months. Of the 51 procedures, 48 (94%) were performed on outpatients with enema preparation and little or no sedation. A median of three procedures was performed per patient, with two sessions required for initial control of bleeding. Ten patients (71%) required maintenance therapy for recurrent bleeding from telangiectasias that developed after initial therapy. The mean interval between maintenance sessions was 7 months. No immediate or late complications occurred.

For an idealized inertia-gravity wave, the Stokes drift, defined as the difference in end positions of a fluid parcel as derived in the Lagrangian and Eulerian coordinates, is exactly zero after one wave cycle in a deterministic flow. When stochastic effects are incorporated into the model, nonlinearity in the velocity field changes the statistical properties. Better understanding of the statistics of a passive tracer, such as the mean drift and higher order moments, leads to more accurate predictions of the pattern of Lagrangian mixing in a realistic environment. In this paper, we consider the inertia-gravity wave equation perturbed by white noise and solve the Fokker–Planck equation to study the evolution in time of the probability density function of passive tracers in such a flow. We find that at initial times the tracer distribution closely follows the nonlinear background flow and that nontrivial Stokes drift ensues as a result. Over finite times, we measure chaotic mixing based on the stochastic me...

The reaction of the anti-B18H22 borane cluster with nickelocene produced several new metallaborane species, [Ni(THF)4(H2O)2][B18H20Ni(η5-C5H5)]2 (1a), [B18H20Ni(η5-C5H5)] (1b) and [N(CH3)4][B18H19(2-THF)Ni(η5-C5H5)] (2), in relatively high yields. These new complexes were fully characterized by multinuclear NMR (1H, 13C, 11B), IR and UV-Vis spectroscopy. Single-crystal X-ray diffraction analyses of complexes 1a and 2 confirmed their structures as 19-vertex conjuncto-metallaborane clusters. The structures consist of ten-vertex nido-borane subunits edge-shared with eleven-vertex nido-cluster subunits. In compound 2, formed through the THF reflux of compound 1, a THF molecule was found to coordinate at the 2-position of the borane framework.