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Biomedical subjects

M Bulmer

Publications and source records attributed to M Bulmer.

33 records · Page 2Linked to original sources
PubMed1989

Structural instability of models of sexual selection.

Models for sexual selection by the coevolution of female preference and a male trait have as a generic feature the existence of a neutrally stable line of equilibria up and down which the system can drift at random. However, this feature is structurally unstable since it is destroyed by introducing either mutation or weak direct selection on female preference into the model, to be replaced by a single equilibrium (or a finite set of disconnected equilibria). This process is investigated in detail under a simple but general population genetic model. It is concluded that the level of female preference is determined by mutation, selection, and genetic drift acting directly on it, and drags the male trait along with it along the line of equilibria. More attention should be paid to selective forces acting directly on female preference.

Biological Evolution↗
PubMed1989

Estimating the variability of substitution rates.

Suppose that amino acid or nucleotide data are available for a homologous gene in several species which diverged from a common ancestor at about the same time and that substitution rates between all pairs of species are calculated, correcting as necessary for multiple substitutions and for back and parallel substitutions. The variances and covariances of these corrected substitution rates are evaluated, and are used to construct a new test for uniformity (constancy of the molecular clock) and to find the best estimates of substitution rates in individual lineages with their standard errors. A substantial bias may arise if the effect of correcting the pairwise substitution rates is ignored.

Amino Acids↗
PubMed1988

Codon usage and intragenic position.

Data on codon usage bias in E. coli are re-examined with respect to intragenic position. The bias is less extreme near the beginning than in the rest of the gene, particularly in highly expressed genes. This is contrary to the previous finding that there is a linear decline in codon usage bias with position along weakly expressed genes but little or no change in bias along highly expressed genes. The effect is not confined to genes coding for proteins with leader peptides, as suggested earlier (Burns and Beacham, 1985). There is some evidence of a similar but smaller effect in yeast.

Codon↗
PubMed1988

Selective differences among translation termination codons.

The frequency of use of the three alternative translation termination codons has been examined in 165 Escherichia coli, 52 Bacillus subtilis and 106 Saccharomyces cerevisiae genes. Genes were first categorised according to their degree of bias in sense codon usage. In each species there is a very strong bias in favour of UAA (over UAG and UGA) in genes where sense codon usage is highly biased. This bias declines, principally with an increase in the use of UGA, in genes with lower sense codon bias. It appears that selection operating during translation may maintain the bias in stop codon usage. Such selection could result from the greater availability of UAA-cognate release factor(s), or from a lower frequency of translational readthrough at UAA.

Bacillus subtilis↗
PubMed1988

Sex ratio evolution in lemmings.

In the varying lemming, Dicrostonyx torquatus, numerous XY females occur due to the X-linked mutation X*. Gileva (1987) has shown that there is also segregation distortion in males, with the segregation ratio for Y sperm being about 0.56, which has a significant effect on the sex ratio and the frequency of XY females. A theoretical analysis shows that this degree of segregation distortion is expected to evolve in the Dicrostonyx system under random mating, provided that reproductive compensation for the loss of YY zygotes by XY females is largely an automatic process due to reduced competition between the surviving embryos. The evolution of segregation distortion makes it unlikely that X* is an adaptation to allow a female-biased sex ratio in response to population structure.

Animals↗
PubMed1988

Research policy and review 23. The view of academic social scientists on the 1991 U.K. Census of Population: a report of the Economic and Social Research Council Working Group.

This is a report on the survey conducted for the United Kingdom Census Office by the Economic and Social Research Council (ESRC) concerning the 1991 census. "The primary task was to solicit views on the priority which [academic social scientists] attached to the proposed topics to be covered by the Census and to ascertain their views on the changes in question wording which are under consideration.... Views were also sought on different methods for giving academics access to individual-level data from the 1991 Census."

Attitude↗
PubMed1987

A statistical analysis of nucleotide sequences of introns and exons in human genes.

DNA sequences of 56 human genes for which information on both exons and introns was available were examined. The variance in G+C content among genes is estimated and shown to be substantial. There is a high correlation in G+C content between exons and introns within the same gene. The dinucleotide frequencies of introns are similar to those of intergenic spacer regions and are in reasonable agreement with predictions from substitution rates estimated from pseudogenes, except that the observed deficiency of TA doublets is not predicted. Duplicated bases also show a frequency greater than the expectation under independence. There is marked variability among genes in the frequency of the doublet CG relative to its expectation under independence. This variation is evolutionarily conserved and is correlated with the G+C content. Pseudogenes behave as if they are in a low -G+C, CG-deficient part of the genome, although the genes from which they arose are variable in these respects.

Base Composition↗
PubMed1986

Neighboring base effects on substitution rates in pseudogenes.

Substitution rates in pseudogenes can be used to estimate the frequencies of different types of mutation on the assumption that pseudogenes are not subject to selective constraints. These rates are used here to investigate the effect of neighboring bases on mutation rates. There is a marked increase in the frequency of transitions, though not of transversions, from the doublet CG. There are also some smaller effects of neighboring bases on the frequencies of transitions from adenine and thymine. The results are used to predict dinucleotide frequencies in a stretch of DNA subject to no selective constraints and to investigate the possibility of non-randomness in the usage of stop codons.

Animals↗
PubMed1986

A controversial census topic: race and ethnicity in the British census.

"This paper examines attempts to collect data on a politically controversial topic, race and ethnicity, in the British Census of Population in the post-war period. It discusses an indirect, proxy method of inferring race or ethnicity by asking for the country of birth of the respondent and of his parents, and a direct question where the respondent is asked to identify his racial or ethnic group. Different versions of the direct question are examined, as is the 1979 Census test, which resulted in considerable public resistance to the question. Following the exclusion of the direct question from the 1981 Census, the subject was reviewed by the Parliamentary Home Affairs Committee, the results of whose report--including practical suggestions as to question wording--are discussed."

Censuses↗
PubMed1982

Are pseudo-patient studies justified?

Pseudo-patient studies are studies in which a medical sociologist or anthropologist masquerades as a patient. Medical treatment is sought without revealing that the 'patient' is really a covert research worker. When access has thus been gained to a medical setting--typically a hospital ward--social interaction between medical staff and patients is then observed over a period of days or weeks. Important studies have been carried out in this way of psychiatric treatment and of the care of the terminally-ill. Is the use of the method justified? What ethical problems does its use raise? How do the undoubted advantages of the approach compare with the clear drawbacks and objections which can be made to its use?

Behavioral Research↗
PubMedDate not supplied

Coevolution of codon usage and transfer RNA abundance.

The use of synonymous codons is strongly biased in the bacterium Escherichia coli and yeast, comprising both bias between codons recognized by the same transfer RNA and bias between groups of codons recognized by different synonymous tRNAs. A major determinant of the second sort of bias is tRNA content, codons recognized by abundant tRNAs being used more often than those recognised by rare tRNAs, particularly in highly expressed genes, probably owing to selection at the level of translation against codons recognized by rare tRNAs. Conversely, codon usage is likely to exert selection pressure on tRNA abundance. Here I develop a model for the coevolution of codon usage and tRNA abundance which explains why there are unequal abundances of synonymous tRNAs leading to biased usage between groups of codons recognized by them in unicellular organisms.

Biological Evolution↗