The over-dispersion between cells of chromosomal aberrations.
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Chromosome Aberrations↗
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The dynamics of infection of Tribolium confusum by Hymenolepis diminuta: the influence of infective-stage density and spatial distribution.
The mean parasite burden of a population of Tribolium confusum is shown to rise to a plateau as the exposure density of infective eggs of Hymenolepis diminuta increases. The level of this plateau is shown to be dependent on the nutritional status of the host population, being depressed from approximately 18 cysticeroids/beetle in hosts which have been starved prior to experimentation, to approximately 2 cysticercoids/beetle in satiated hosts. A simple model is used to describe the shape of this infection functional response in terms of the predator-prey interaction between hosts (T. confusum) and parasite infective stages (H. diminuta eggs). The distribution of successful infections/host is shown to be over-dispersed, even when hosts are exposed to infective stages arranged in a uniform spatial pattern. The over-dispersion of parasite numbers/host is shown to become more severe as the spatial pattern of infective stages changes from under-dispersed, through random, to over-dispersed. Experimental results are discussed in relation to the dynamics of parasite-host interactions, in which infection takes place by host ingestion of a free-living infective stage.
Feeding Behavior↗
A divide and conquer strategy for recapitulating whole genome 3D structure using Hi-C data.
The three dimensional (3D) spatial organization of the genome is closely linked to biological functions and can be captured by Hi-C assays through interrogating genome-wide chromatin interactions. Methodologies for inferring 3D structures from Hi-C data summarized as a two-dimensional (2D) contact matrix can be broadly placed within the paradigms of optimization-based and sampling-based. Many optimization-based methods are capable of constructing whole genome 3D structures but do not account for spatial dependency in the 2D data matrix nor cell heterogeneity in bulk Hi-C data, which provide an average over millions of cells. Sampling-based methods, on the other hand, are probabilistic model-based and can account for not only dependency, heterogeneity, but also other features inherent in Hi-C data, such as over-dispersion and sparsity. However, whole-genome 3D structure recapitulation is too computationally expensive for sampling-based methods, while chromosome-by-chromosome strategies for sampling-based methods ignore important information on inter-chromosomal contacts. To address these issues, we propose the truncated Random effect EXpression-cut and paste (tREX-cap) method, which applies the tREX model within a divide and conquer strategy. The resulting method inherits the good data-feature-cognizant properties of tREX and, in the meantime, can efficiently infer the whole genome 3D structure. We demonstrate the performance of tREX-cap through an extensive simulation study and analyses of a Hi-C lymphoblastoid dataset and a Hi-C IMR90 dataset.
Humans↗
The cytogenetic effect of bleomycin on human peripheral lymphocytes in vitro and in vivo.
The cytogenetic effect of bleomycin (BLM) in human lymphocytes was studied after exposure to different doses during the G0 and G2 phases. BLM produced a marked specific effect on the cell cycle. The main aberration types after exposure in tg0 were dicentrics and deletions; and after exposure in G2, open chromatid breaks. A linear dose--response was calculated for all these aberration types as well as for the number of aberrant cells. In the G2 experiments, partially and totally pulverized cells also increased linearly with dose. The intercellular distributions of the most frequent aberration types after exposure in G0 and G2--the dicentrics and chromatid breaks, respectively--showed over-dispersion. These results show that the cytogenetic effect of BLM may be compared with that of densely ionizing irradiation. Preliminary results of chromosome analysis of three cancer patients in the course of BLM therapy showed effects similar to those in the G0 experiments.
Bleomycin↗
Experimental studies of infection dynamics: infection of the definitive host by the cercariae of Transversotrema patialense.
The number of cercariae of Transversotrema patialense which attach to the fish host Brachydanio rerio, during a fixed exposure period, is shown to be directly proportional to cercarial density within an experimental infection arena. The distribution of successful infections/host is shown to change from a random pattern to an over-dispersed form as cercarial exposure density or duration of host exposure to infection increases. A stochastic simulation model is used to demonstrate that small differences in host susceptibility to infection, within a population of hosts, can generate patterns of dispersion in parasite numbers/host similar to those observed in the experimental studies. Differences in host behaviour, during the period of exposure to infection, are thought to generate variability in host susceptibility to cercarial infection.
Animals↗
Population dynamics of snail infection by miracidia.
The essential biological features of snail infection by miracidia are incorporated into a simple model which describes the rate of change with respect to time of the number of miracidial infections/host. The model is based on the assumption that the net rate of infection is directly proportional to the density of both miracidia and hosts. Empirical evidence is provided to support this assumption. The basic framework of the model is expanded to take into account demographic stochasticity in infection and is used to predict the percentage of snails that become infected after exposure to a known number of miracidia for a set period of time. The influence of miracidial mortalities and age-dependent infectivity are examined and theoretical predictions are compared with a range of experimental results. Underlying heterogeneity in the distribution of the number of infections/snail is shown to generate an artifactual decrease in infection rates as exposure density rises, if rate estimation procedures are based on an assumption of randomness. Empirical evidence is presented to illustrate the generation of over-dispersion in the number of miracidial infections/snail under tightly controlled laboratory conditions, using supposedly homogeneous snail populations. Biological causes for underlying patterns of heterogeneity are discussed in relation to snail susceptibility to infection and 'attractiveness' to infective stages.
Animals↗
Genetic linkage disequilibrium of deleterious mutations in threatened mammals.
The impact of negative selection against deleterious mutations in endangered species remains underexplored. Recent studies have measured mutation load by comparing the accumulation of deleterious mutations, however, this method is most effective when comparing within and between populations of phylogenetically closely related species. Here, we introduced new statistics, LDcor, and its standardized form nLDcor, which allows us to detect and compare global linkage disequilibrium of deleterious mutations across species using unphased genotypes. These statistics measure averaged pairwise standardized covariance and standardize mutation differences based on the standard deviation of alleles to reflect selection intensity. We then examined selection strength in the genomes of seven mammals. Tigers exhibited an over-dispersion of deleterious mutations, while gorillas, giant pandas, and golden snub-nosed monkeys displayed negative linkage disequilibrium. Furthermore, the distribution of deleterious mutations in threatened mammals did not reveal consistent trends. Our results indicate that these newly developed statistics could help us understand the genetic burden of threatened species.
Animals↗
Distribution of sibship size in families manifesting a genetically determined disorder.
The effect on sibship size distribution of the birth of a child with a genetical defect is considered for several different conditions. Family size continues to be over-dispersed in such cases, rather than showing any sign of reduced variation, though theoretical expectations about the correlation between numbers of normal and affected children are not well-supported by the data.
Chromosome Aberrations↗
The detection of genetical influences on human family size.
The genetics of human family size is not readily susceptible to analysis. Some of the problems in its investigation are discussed, together with methods for overcoming them. In particular, the problem of obtaining a satisfactory model which will account for both the low heritability of family size and its over-dispersed distribution is examined in detail.
Family↗
[The filaria Dipetalonema dessetae: phenomena of regulation and parasite yield in the Aedes vector].
Numerical observations were made on the various steps of the cycle of Dipetalonema dessetae in Aedes aegypti: -- ingestion of microfilariae: the numbers of the ingested microfilariae correspond to a negative binomial distribution, but the over-dispersion is less important than in the Bancroft's filaria as observed by Pichon; in this last case the microfilariae are thicker and thus are more slowed in the capillari; -- crossing of the stomach wall: the "limitation" is caused by a precociously established stomacal barrier (2nd hour); however, this barrier is not perfect and allows some microfilariae to infiltrate; -- larval development and migration towards the head: in the well fed mosquitoes, all the microfilariae in the hemocoel reach the infective stage, but less rapidly in the heavily infected mosquitoes; 50 per cent of the microfilariae migrate towards the head, not depending with the level of infection. In this couple filaria-vector, the regulation of the transmission is depending nearly exclusively with the stomacal "limitation" and secondarily with different speeds of the development. The feeding of the mosquito -- preimago or adult -- is an essential factor for vector efficiency.
Adipose Tissue↗