A review of algorithms for medical image segmentation and their applications to the female pelvic cavity

This paper aims to make a review on the current segmentation algorithms used for medical images. Algorithms are classified according to their principal methodologies, namely the ones based on thresholds, the ones based on clustering techniques and the ones based on deformable models. The last type is focused on due to the intensive investigations into the deformable models that have been done in the last few decades. Typical algorithms of each type are discussed and the main ideas, application fields, advantages and disadvantages of each type are summarised. Experiments that apply these algorithms to segment the organs and tissues of the female pelvic cavity are presented to further illustrate their distinct characteristics. In the end, the main guidelines that should be considered for designing the segmentation algorithms of the pelvic cavity are proposed.     

A comparison of alternative methods to compute conditional genotype probabilities for genetic evaluation with finite locus models

An increased availability of genotypes at marker loci has prompted the development of models that include the effect of individual genes. Selection based on these models is known as marker-assisted selection (MAS). MAS is known to be efficient especially for traits that have low heritability and non-additive gene action. BLUP methodology under non-additive gene action is not feasible for large inbred or crossbred pedigrees. It is easy to incorporate non-additive gene action in a finite locus model. Under such a model, the unobservable genotypic values can be predicted using the conditional mean of the genotypic values given the data. To compute this conditional mean, conditional genotype probabilities must be computed. In this study these probabilities were computed using iterative peeling, and three Markov chain Monte Carlo (MCMC) methods – scalar Gibbs, blocking Gibbs, and a sampler that combines the Elston Stewart algorithm with iterative peeling (ESIP). The performance of these four methods was assessed using simulated data. For pedigrees with loops, iterative peeling fails to provide accurate genotype probability estimates for some pedigree members. Also, computing time is exponentially related to the number of loci in the model. For MCMC methods, a linear relationship can be maintained by sampling genotypes one locus at a time. Out of the three MCMC methods considered, ESIP, performed the best while scalar Gibbs performed the worst.     

Perturbation expansions of multilocus fixation probabilities for frequency-dependent selection with applications to the Hill-Robertson effect and to the joint evolution of helping and punishment

Natural populations are of finite size and organisms carry multilocus genotypes. There are, nevertheless, few results on multilocus models when both random genetic drift and natural selection affect the evolutionary dynamics. In this paper we describe a formalism to calculate systematic perturbation expansions of moments of allelic states around neutrality in populations of constant size. This allows us to evaluate multilocus fixation probabilities (long-term limits of the moments) under arbitrary strength of selection and gene action. We show that such fixation probabilities can be expressed in terms of selection coefficients weighted by mean first passages times of ancestral gene lineages within a single ancestor. These passage times extend the coalescence times that weight selection coefficients in one-locus perturbation formulas for fixation probabilities. We then apply these results to investigate the Hill-Robertson effect and the coevolution of helping and punishment. Finally, we discuss limitations and strengths of the perturbation approach. In particular, it provides accurate approximations for fixation probabilities for weak selection regimes only (Ns?1), but it provides generally good prediction for the direction of selection under frequency-dependent selection.     

Validation of bone surface modification models for inferring fossil hominin and carnivore feeding interactions, with reapplication to FLK 22, Olduvai Gorge, Tanzania

Resolving the issue of how Early Stone Age hominins acquired large mammal carcasses requires information on their feeding interactions with large carnivores. This ecological information and its behavioral and evolutionary implications are revealed most directly from the tooth, cut, and percussion marks on bone surfaces generated by hominin and carnivore feeding activities. This paper employs a bootstrap method, a form of random resampling with replacement, to refine published neotaphonomic models that use the assemblage-wide proportions of long bones bearing feeding traces to infer the sequences in which Plio-Pleistocene hominins and carnivores accessed flesh, marrow, and/or grease from carcasses. Results validate the sensitivity of the models for inferring hominin feeding ecology, which have been questioned on grounds shown here to be unfounded. The bootstrapped feeding trace models are applied to the late Pliocene larger mammal fossil assemblage from FLK 22 (Zinjanthropus site), Olduvai Gorge, Tanzania. High frequencies of tooth and percussion marking on long bone midshaft fragments from FLK 22 are most consistent with those feeding trace models that simulate hominin scavenging from carcasses defleshed by carnivores, while cut mark data indicate that hominins more often had access to upper forelimb flesh than upper hind limb flesh. Together, the bone surface modification data indicate that hominins typically gained secondary access to partially defleshed carnivore kills, but they also allow for the possibility of some carcasses being processed only by carnivores and only by hominins.     

Intergenic sequences of clustered tRNA genes: new type of genetic marker for phylogenetic studies, with application to the taxonomy of liverworts

We have established a new type of genetic marker in Pellia liverworts that can be used to differentiate between closely related species within this genus. The Pellia intergenic sequences spanning the tandemly repeated nuclear tRNALeu genes were amplified using the PCR technique and, in the case of Pellia neesiana, the tRNALeu tandem region was cloned and sequenced. The length comparison of the intergenic regions allowed for the identification of a number of Pellia species. Additional experiments suggest that this marker can be used to differentiate other species of liverworts and mosses.     

A comparison of Glossina morsitans centralis originating from Tanzania and Zambia, with respect to vectorial competence for pathogenic Trypanosoma species, genetic variation and inter-colony fertility

wo laboratory strains of Glossina morsitans centralis originating from different fly-belts (one from Singida, in Tanzania, and the other from Mumbwa, in Zambia) were compared with respect to vectorial competence for pathogenic Trypanosoma species, genetic variation and inter-colony fertility. The vectorial competence of G.m.centralis of Tanzanian origin for Trypanosoma vivax and T.congolense is similar to, whereas for T.brucei brucei it is lower than the colony of Zambian origin. Nevertheless, these two laboratory strains of G.m.centralis showed levels of susceptibility to the three pathogenic Trypanosoma species which were much greater than previously observed in laboratory colonies of other Glossina species. Electrophoresis of fifteen enzymes revealed that the two colonies differ significantly in allele frequencies at only three loci that are relatively close together on one of the autosomes. Hybridization experiments revealed that G.m.centralis from the two fly-belts are consubspecific.     

Individual optimization efforts and population dynamics: a mathematical model for the evolution of resource allocation strategies, with applications to reproductive and mating systems

We develop a formal framework for the optimal allocation of limited resources that includes and clarifies the interplay between individual optimization and the resulting effects at the population level. As an example, in regard to the evolution of sexual recombination, the paradox of the twofold cost of sex is avoided by distinguishing between the evolution of recombination and the subsequent emergence and stability of different mating types as a result of individual optimization within a population that benefits from recombination.