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Biomedical subjects

D Greig

Publications and source records attributed to D Greig.

At least 19 recordsLinked to original sources
PubMed2003

A role for the mismatch repair system during incipient speciation in Saccharomyces.

The cause of reproductive isolation between biological species is a major issue in the field of biology. Most explanations of hybrid sterility require either genetic incompatibilities between nascent species or gross physical imbalances between their chromosomes, such as rearrangements or ploidy changes. An alternative possibility is that genomes become incompatible at a molecular level, dependent on interactions between primary DNA sequences. The mismatch repair system has previously been shown to contribute to sterility in a hybrid between established yeast species by preventing successful meiotic crossing-over leading to aneuploidy. This system could also promote or reinforce the formation of new species in a similar manner, by making diverging genomes incompatible in meiosis. To test this possibility we crossed yeast strains of the same species but from diverse historical or geographic sources. We show that these crosses are partially sterile and present evidence that the mismatch repair system is largely responsible for this sterility.

Base Pair Mismatch↗
PubMed2001

Outcrossed sex allows a selfish gene to invade yeast populations.

Homing endonuclease genes (HEGs) in eukaryotes are optional genes that have no obvious effect on host phenotype except for causing chromosomes not containing a copy of the gene to be cut, thus causing them to be inherited at a greater than Mendelian rate via gene conversion. These genes are therefore expected to increase in frequency in outcrossed populations, but not in obligately selfed populations. In order to test this idea, we compared the dynamics of the VDE HEG in six replicate outcrossed and inbred populations of yeast (Saccharomyces cerevisiae). VDE increased in frequency from 0.21 to 0.55 in four outcrossed generations, but showed no change in frequency in the inbred populations. The absence of change in the inbred populations indicates that any effect of VDE on mitotic replication rates is less than 1%. The data from the outcrossed populations best fit a model in which 82% of individuals are derived from outcrossing and VDE is inherited by 74% of the meiotic products from heterozygotes (as compared with 50% for Mendelian genes). These results empirically demonstrate how a host mating system plays a key role in determining the population dynamics of a selfish gene.

Chromosome Mapping↗
PubMed1998

The effect of sex on adaptation to high temperature in heterozygous and homozygous yeast.

Most explanations for the evolutionary maintenance of sex depend on the assumption that sex produces variation by recombining parental haplotypes in the offspring. Therefore, meiosis is expected to be useful only in heterozygotes. We tested this assumption by competing sexual strains of yeast against constitutive asexuals in a hot (37 degrees C) culture for 500 generations, in either heterozygous or homozygous genetic backgrounds. We found that there was an initial cost of sex for all the sexual strains, which was indicated by a sharp increase in the proportion of asexuals after the induction of sex. The cost was larger in the heterozygotes than in the homozygotes, probably because of recombinational load. However, in two of the three heterozygote backgrounds, after the initial success of the asexuals, the remaining sexuals eventually drove them out of the population. These two heterozygotes also suffered the largest initial cost of sex. In the other heterozygote and in the three homozygote backgrounds it appeared to be a matter of chance whether sexuals or asexuals won. The average relative fitness increased in all the strains, but the increase was largest in the two strains that showed both the clearest advantage and the largest cost of sex. We conclude that these results are consistent with the traditional view that sex has a short-term cost but a long-term benefit.

Adaptation, Biological↗
PubMed1997

Contact dermatitis from cetostearyl alcohol.

Emulsifiers are an uncommon cause of allergic contact dermatitis. Five cases of allergic contact dermatitis to cetostearyl alcohol are presented. In all five cases, multiple positive reactions to other allergens were present, usually topical corticosteroid creams.

Adult↗
PubMed1990

Validation of a method for the rapid diagnosis of urinary tract infection suitable for use in general practice.

A combination of reagent strip testing and examining urine appearance can be used to screen out noninfected cases before urine specimens are sent to the laboratory. A validation of this method was carried out in a microbiology laboratory using 970 specimens received over a three-week period. When the tests for nitrite, blood and protein on N-Multistix reagent strips (Ames) were all negative in a clear urine then the predictive value for the absence of bacteriuria was 98.5%. Positive strip tests in a turbid urine detected 80.1% of infections. On the basis of these findings it is recommended that general practitioners test the urine samples of all patients with suspected urinary tract infections by this method and only send to the laboratory those specimens with positive findings. Using this method the routine laboratory workload involved in testing urine specimens would be reduced by 40%, instant results would be available in the general practitioner's surgery and the patient would receive immediate and appropriate treatment.

Bacteriuria↗
PubMed1987

Blister beetle dermatosis in New Zealand.

Seventy-four New Zealand Army personnel with a distinctive bullous dermatosis caused by an endemic beetle are described. These are the first reported cases of this condition in New Zealand. The beetle, Thelyphassa lineata (Fabricius) belonging to the family Oedemeridae was shown to be a vesicant species, as skin contact induced blisters in volunteers. This is a previously unrecognised property of this species.

Animals↗