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A MacLeod

Publications and source records attributed to A MacLeod.

18 recordsLinked to original sources
PubMed1992

Minisatellite variant repeat (MVR) mapping: analysis of 'null' repeat units at D1S8.

Minisatellite variant repeat mapping by PCR (MVR-PCR) is a new approach to studying variation in human DNA which analyses interspersion patterns of variant repeats within minisatellite arrays. MVR-PCR has been applied to the hypervariable human minisatellite D1S8 which contains two major classes of variant 29bp repeat units designated a-type and t-type. The MVR-PCR assay uses a- or t-type specific primers, together with an amplimer at a fixed site in the DNA flanking the minisatellite, to reveal the interspersion patterns of variant repeats along an allele. Extreme levels of variation are seen both in the internal structures of individual alleles and in the digital code generated from the two superimposed alleles in total genomic DNA. However, occasional repeat units fail to amplify in MVR-PCR, signifying the existence of further repeat sequence variants termed 'null' or O-type repeats. Although not significant in individual identification, correct genotyping of null repeats is important when using MVR digital codes in parentage analysis. We have therefore characterised these null repeats and show that most null repeats share a common variant repeat sequence. We discuss the possible origins of null repeats and their application to paternity testing and the analysis of minisatellite evolution.

Alleles↗
PubMed1991

Minisatellite repeat coding as a digital approach to DNA typing.

Most DNA typing systems used in forensic and legal medicine assay allelic length variation at tandem repetitive DNA regions such as minisatellites. A simple alternative approach that displays patterns of variant repeat units along minisatellite alleles is described here. This produces DNA profiles as extraordinarily variable digital sequences appropriate for forensic investigations, including computer databasing, and for analysing allele diversity and the role of recombination in minisatellite instability.

Base Sequence↗
PubMed1991

Principles and recent advances in human DNA fingerprinting.

Since 1985, DNA typing systems have played an increasingly important role in many aspects of human genetics, most notably in forensic and legal medicine. This article reviews the development of multilocus and single locus minisatellite DNA probes, and more recently the use of PCR to amplify hypervariable DNA loci, as well as discussing the biological properties of the unstable regions of DNA which form the basis of almost all DNA fingerprinting systems.

Base Sequence↗
PubMed1990

"Major minisatellite loci" detected by minisatellite clones 33.6 and 33.15 correspond to the cognate loci D1S111 and D7S437.

G. Chimini et al. (1989, Genomics 5: 316-324) have recently reported that the two multilocus DNA fingerprinting probes 33.6 and 33.15 each detect a single major site in the human genome, at 1q23 and 7q35-q36, respectively, and speculate that these sites represent particularly large loci homologous to these probes. However, the human minisatellite loci cloned in 33.6 and 33.15 can themselves be assigned by somatic cell hybrid analysis to 1cen-q24 and 7q31.3-qter, respectively, corresponding to the "major loci" of Chimini et al. Furthermore, under their hybridization conditions, both 33.6 and 33.15 act largely as locus-specific minisatellite probes. The "major minisatellite loci" postulated by Chimini et al. do not therefore appear to represent major localized clusters of minisatellites in the human genome, but rather the loci cloned in 33.6 and 33.15.

Base Sequence↗
PubMed1990

A procedure for measuring auditory and audio-visual speech-reception thresholds for sentences in noise: rationale, evaluation, and recommendations for use.

The strategy for measuring speech-reception thresholds for sentences in noise advocated by Plomp and Mimpen (Audiology, 18, 43-52, 1979) was modified to create a reliable test for measuring the difficulty which listeners have in speech reception, both auditorily and audio-visually. The test materials consist of 10 lists of 15 short sentences of homogeneous intelligibility when presented acoustically, and of different, but still homogeneous, intelligibility when presented audio-visually, in white noise. Homogeneity was achieved by applying phonetic and linguistic principles at the stage of compilation, followed by pilot testing and balancing of properties. To run the test, lists are presented at signal-to-noise ratios (SNRs) determined by an up-down psychophysical rule so as to estimate auditory and audio-visual speech-reception thresholds, defined as the SNRs at which the three content words in each sentence are identified correctly on 50% of trials. These thresholds provide measures of a subject's speech-reception abilities. The difference between them provides a measure of the benefit received from vision. It is shown that this measure is closely related to the accuracy with which subjects lip-read words in sentences with no acoustical information. In data from normally hearing adults, the standard deviations (s.d.s) of estimates of auditory speech reception threshold in noise (SRTN), audio-visual SRTN, and visual benefit are 1.2, 2.0, and 2.3 dB, respectively. Graphs are provided with which to estimate the trade-off between reliability and the number of lists presented, and to assess the significance of deviant scores from individual subjects.

Adolescent↗
PubMed1989

Novel benzodiazepine receptor partial agonists: oxadiazolylimidazobenzodiazepines.

The synthesis and biochemical evaluation of a series of oxadiazole derivatives of imidazobenzodiazepines related to the benzodiazepine antagonist Ro 15-1788 (2a) are reported. Although the oxadiazole ring is seen as an isosteric replacement for the ester linkage, significant differences in structure-activity trends were observed. Specifically, oxadiazoles 9-12 invariably had increased receptor efficacy (as witnessed by measurements of the GABA shift) relative to the corresponding ester. Additionally, and in direct contrast to the classical agonists such as diazepam, affinity for the benzodiazepine receptor was enhanced by a 7- rather than 8-halo substituent. The results are discussed in terms of a six-point receptor-binding model originally based on the X-ray structure of 2a. For comparison, the crystal structures of two representative oxadiazole derivatives, 10h and 12o, having a 6-oxo and 6-phenyl group, respectively, were determined and the data incorporated into a modified binding model to account for the greater efficacy of these compounds. It is concluded that the antagonist behavior of 2a relies upon the hydrogen-bond-acceptor properties of the ester carbonyl oxygen whereas for the oxadiazole series this site is localized at the imidazole nitrogen.

Animals↗
PubMed1988

Starvation and nutrient resuscitation of Klebsiella pneumoniae isolated from oil well waters.

Klebsiella pneumoniae isolated from oil well waters reduced in size in response to nutrient starvation. The cells remained viable during starvation and later were able to grow rapidly when stimulated by nutrients. The heterotrophic potential, culture absorbance and extracellular polysaccharide production decreased during cell starvation whereas an initial increase in colony-forming units was observed on agar plates. Transmission electron microscopy (TEM) after 24 d revealed that the cells had changed to small rods or cocci between 0.5 by 0.25 micron and 0.87 by 0.55 micron. When transferred to half-strength brain heart infusion medium, TEM showed cell division and rod-shaped cells after 45 min and full resuscitation within 4 h. Cell response was much slower in sodium citrate medium and resuscitation took 8 h.

Bacterial Adhesion↗
PubMed1987

Quantifying the contribution of vision to speech perception in noise.

The intelligibility of sentences presented in noise improves when the listener can view the talker's face. Our aims were to quantify this benefit, and to relate it to individual differences among subjects in lipreading ability and among sentences in lipreading difficulty. Auditory and audiovisual speech-reception thresholds (SRTs) were measured in 20 listeners with normal hearing. Sixty sentences, selected to range in the difficulty with which they could be lipread (with vision alone) from easy to hard, were presented for identification in white noise. Using the ascending method of limits, the SRT was defined as the lowest signal-to-noise ratio at which all three 'key words' in each sentence could be identified correctly. Measured as the difference in dB between auditory-alone and audiovisual SRTs, 'audiovisual benefit' averaged 11 dB, ranging from 6 to 15 dB among subjects, and from 3 to 22 dB among sentences. As predicted, audiovisual benefit is a measure of lipreading ability. It was highly correlated with visual-alone performance (n = 20, r = 0.86, P less than 0.01). Likewise, those sentences which were easiest to lipread gave a higher measure of benefit from vision in audiovisual conditions than did sentences that were hard to lipread (n = 60, r = 0.92, P less than 0.01). The results establish the basis of an efficient test of speech-reception disability in which measures are freed from the floor and ceiling effects encountered when percentage correct is used as the dependent variable.

Adult↗
PubMed1986

Diagnostic utility of lymphocyte subset analysis in AIDS case finding.

Abnormalities of lymphocyte subsets, especially low absolute number of helper T cells, are characteristically present in acquired immune deficiency syndrome (AIDS). Similar abnormalities can be found in patients with persistent generalized lymphadenopathy (PGL) or AIDS-related complex (ARC) and, to a lesser degree, in asymptomatic people who have been exposed to human T-lymphotropic virus type III (HTLV-III). Nevertheless, there appears to be a widespread perception that lymphocyte subset analysis may be useful in AIDS case finding within high-risk groups. We evaluated the diagnostic utility of absolute number of helper T cells and ratio of helper to suppressor T cells in 33 patients with AIDS, 43 patients with PGL who had been referred for lymph node biopsy, 90 patients with PGL and 195 male homosexual controls. At conventional cutoff levels the tests did not appear to revise the probability of AIDS upward to any clinically significant degree when the pretest probability of AIDS was low. Lymphocyte subset analysis does not appear to be a cost-effective method of AIDS case finding in identified groups at risk in which the prevalence of AIDS is low.

Acquired Immunodeficiency Syndrome↗
PubMed1978

Clinical experiences in free flap transfer.

In this series of 62 free flap transfers, 48 (80%) have been successful. There have been a significant number of vascular complications, 39% of which the majority were arterial thrombosis. Fifty per cent of those which thrombosed were salvaged on exploration and revision of the vessels. The frequency of complications has diminished with experience but they remain significantly high. Free flap surgery demands considerable expertise in both donor site dissection and microvascular technique. Two surgeons with microvascular experience, each with adequate assistance, are preferred and ready availability of operating room is essential. Close postoperative observation and readiness to revise anastomoses are equally important. About 50% of failed free flap sites have been repaired by application of split skin grafts.

Adolescent↗