Biomedical subjects

C Neuhauser

Publications and source records attributed to C Neuhauser.

5 recordsLinked to original sources

PubMed1999

The ancestral graph and gene genealogy under frequency-dependent selection.

Minority-advantage frequency-dependent selection has been proposed as the cause for the high level of observed polymorphism in some self/nonself-recognition systems. We present a mathematically rigorous derivation of the ancestral graph for a sample of genes that evolved according to a haploid infinite-alleles model of minority-advantage frequency-dependent selection. In the case of sufficiently weak selection, the gene genealogy can be extracted from the ancestral graph. We demonstrate that the gene genealogy under this model is identical to that obtained for a diploid model with heterozygote advantage. The case of strong selection is exemplified by a one-locus haploid self-incompatibility system; in this context, we investigate the number of alleles that can be maintained in a spatial versus a non-spatial habitat. Finally, we compare gametophytic self-incompatibility to the haploid self-incompatibility model.

Gene Frequency↗

PubMed1998

Habitat Destruction and Competitive Coexistence in Spatially Explicit Models with Local Interactions.

We investigate the competition-colonization trade-off in a two-species competition model in various heterogeneous environments. The competitiveness of species is hierarchically ordered and the dynamics of the model are described by spatially local interactions of individuals. The size of the local neighborhood may depend on the species. The habitat consists of inhabitable and permanently destroyed sites. It was previously observed (Nee & May, 1992; Tilman et al., 1994, 1997) that destruction of habitat may aid the inferior species and cause the superior species to go extinct. These conclusions were based on an n-species model in which the spatial arrangement of destroyed sites was ignored. We examine the effects of different spatial arrangements of destroyed sites on survival and coexistence of the two species. We conclude that the spatial arrangement plays an important role and can influence the outcome qualitatively. The key quantity for predicting the outcome of habitat destruction on species survival is the relationship between the mean dispersal distance and the mean distance between inhabitable and destroyed sites. We contrast the hierarchical model with a version of the Lotka-Volterra model of interspecific competition and show that habitat destruction can alter the dominance relationship between species by reducing intraspecific competition.Copyright 1998 Academic Press

Journal Article↗

PubMed1997

Ancestral Processes with Selection

In this paper, we show how to construct the genealogy of a sample of genes for a large class of models with selection and mutation. Each gene corresponds to a single locus at which there is no recombination. The genealogy of the sample is embedded in a graph which we call the ancestral selection graph. This graph contains all the information about the ancestry; it is the analogue of Kingman's coalescent process which arises in the case with no selection. The ancestral selection graph can be easily simulated and we outline an algorithm for simulating samples. The main goal is to analyze the ancestral selection graph and to compare it to Kingman's coalescent process. In the case of no mutation, we find that the distribution of the time to the most recent common ancestor does not depend on the selection coefficient and hence is the same as in the neutral case. When the mutation rate is positive, we give a procedure for computing the probability that two individuals in a sample are identical by descent and the Laplace transform of the time to the most recent common ancestor of a sample of two individuals; we evaluate the first two terms of their respective power series in terms of the selection coefficient. The probability of identity by descent depends on both the selection coefficient and the mutation rate and is different from the analogous expression in the neutral case. The Laplace transform does not have a linear correction term in the selection coefficient. We also provide a recursion formula that can be used to approximate the probability of a given sample by simulating backwards along the sample paths of the ancestral selection graph, a technique developed by Griffiths and Tavare (1994).

Journal Article↗

PubMed1997

The genealogy of samples in models with selection.

We introduce the genealogy of a random sample of genes taken from a large haploid population that evolves according to random reproduction with selection and mutation. Without selection, the genealogy is described by Kingman's well-known coalescent process. In the selective case, the genealogy of the sample is embedded in a graph with a coalescing and branching structure. We describe this graph, called the ancestral selection graph, and point out differences and similarities with Kingman's coalescent. We present simulations for a two-allele model with symmetric mutation in which one of the alleles has a selective advantage over the other. We find that when the allele frequencies in the population are already in equilibrium, then the genealogy does not differ much from the neutral case. This is supported by rigorous results. Furthermore, we describe the ancestral selection graph for other selective models with finitely many selection classes, such as the K-allele models, infinitely-many-alleles models. DNA sequence models, and infinitely-many-sites models, and briefly discuss the diploid case.

Genealogy and Heraldry↗

PubMed1978

Children's concepts of healing: cognitive development and locus of control factors.

This study of young children's understanding of the process of healing indicates that both level of cognitive development and locus of control are relevant factors. The importance of the children's locus of control orienation to their understanding was found to depend upon the interaction of the cognitive level and the complexity of the concept considered.

Attitude to Health↗