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G K Chambers

Publications and source records attributed to G K Chambers.

At least 37 records · Page 2Linked to original sources
PubMed1995

Inference of population subdivision from the VNTR distributions of New Zealanders.

A population sample from people of diverse ethnic origins living in New Zealand serves as a database to test methods for inference of population subdivision. The initial null hypothesis, that the population sample is homogeneous across ethnic groups, is easily rejected by likelihood ratio tests. Beyond this, methods for quantifying subdivision can be based on the probability of drawing alleles identical by descent (FST), probabilities of matching multiple locus genotypes, and occurrence of unique alleles. Population genetic theory makes quantitative predictions about the relation between FST, population sizes, and rates of migration and mutation. Some VNTR loci have mutation rates of 10(-2) per generation, but, contrary to theory, we find no consistent association between the degree of population subdivision and mutation rate. Quantification of population substructure also allows us to relate the magnitudes of genetic distances between ethnic groups in New Zealand to the colonization history of the country. The data suggests that the closest relatives to the Maori are Polynesians, and that no severe genetic bottleneck occurred when the Maori colonized New Zealand. One of the central points of contention regarding the application of VNTR loci in forensics is the appropriate means for estimating match probabilities. Simulations were performed to test the merits of the product rule in the face of subpopulation heterogeneity. Population heterogeneity results in large differences in estimates of multilocus genotype frequencies depending on which subpopulation is used for reference allele frequencies, but, of greater importance for forensic purposes, no five locus genotype had an expected frequency greater than 10(-6). Although this implies that a match with an innocent individual is unlikely, in a large urban area such chance matches are going to occur.

Alleles↗
PubMed1995

Use of spectral analysis to test hypotheses on the origin of pinnipeds.

The evolutionary origin of the pinnipeds (seals, sea lions, and walruses) is still uncertain. Most authors support a hypothesis of a monophyletic origin of the pinnipeds from a caniform carnivore. A minority view suggests a diphyletic origin with true seals being related to the mustelids (otters and ferrets). The phylogenetic relationships of the walrus to other pinniped and carnivore families are also still particularly problematic. Here we examined the relative support for mono- and diphyletic hypotheses using DNA sequence data from the mitochondrial small subunit (12S) rRNA and cytochrome b genes. We first analyzed a small group of taxa representing the three pinniped families (Phocidae, Otariidae, and Odobenidae) and caniform carnivore families thought to be related to them. We inferred phylogenetic reconstructions from DNA sequence data using standard parsimony and neighbor-joining algorithms for phylogenetic inference as well as a new method called spectral analysis (Hendy and Penny) in which phylogenetic information is displayed independently of any selected tree. We identified and compensated for potential sources of error known to lead to selection of incorrect phylogenetic trees. These include sampling error, unequal evolutionary rates on lineages, unequal nucleotide composition among lineages, unequal rates of change at different sites, and inappropriate tree selection criteria. To correct for these errors, we performed additional transformations of the observed substitution patterns in the sequence data, applied more stringent structural constraints to the analyses, and included several additional taxa to help resolve long, unbranched lineages in the tree. We find that there is strong support for a monophyletic origin of the pinnipeds from within the caniform carnivores, close to the bear/raccoon/panda radiation. Evidence for a diphyletic origin was very weak and can be partially attributed to unequal nucleotide compositions among the taxa analyzed. Subsequently, there is slightly more evidence for grouping the walrus with the eared seals versus the true seals. A more conservative interpretation, however, is that the walrus is an early, but not the first, independent divergence from the common pinniped ancestor.

Algorithms↗
PubMed1994

Plasma concentrations of vitellogenin and sex steroids in female tuatara (Sphenodon punctatus punctatus) from northern New Zealand.

Vitellogenesis in tuatara (Sphenodon punctatus) on Stephens Island, New Zealand, at the southern (coolest) end of the geographical range of this species involves a prolonged period of about 3 years of the average 4-year reproductive cycle. These studies used a semiquantitative electrophoretic assay for vitellogenin (Vg). In the present study an ELISA was used to measure plasma levels of Vg in 138 female northern tuatara (S.p. punctatus) on 11 islands at the warmest end of the tuatara's range. Blood samples were collected in late summer-early autumn, just prior to the expected time of ovulation in those females that would nest the following spring. Plasma Vg levels ranged from nondetectable to 2.9 mg/ml but were not significantly correlated with plasma estradiol, testosterone, or progesterone levels. There was also no significant correlation among the three sex steroids. Plasma Vg and hormone levels were further examined as to whether females were ovulating. Incipient ovulation was inferred using endocrinological criteria derived from studies of tuatara on Stephens Island (i.e., elevated plasma testosterone). Plasma levels of Vg differed significantly between inferred ovulators and nonovulators when data for all islands were combined, although similar ranges were observed in the two groups of females (inferred ovulators: nondetectable to 2382 micrograms/ml, mean = 505 +/- 75; inferred nonovulators: nondetectable to 2864 micrograms/ml, mean = 460 +/- 63). Plasma levels of estradiol, but not progesterone, differed significantly between inferred ovulators and nonovulators when data for all islands were combined. Mean levels in inferred ovulators were: estradiol, 157 +/- 16 pg/ml (vs. 34 +/- 5 pg/ml in inferred nonovulators); progesterone, 1.1 +/- 0.2 ng/ml (vs. 0.7 +/- 0.1 ng/ml in inferred nonovulators); and testosterone, 5.6 +/- 0.5 ng/ml (vs. 0.2 +/- 0 ng/ml in inferred nonovulators). Only 37% of the females sampled met the minimum hormonal criteria indicative of ovulation. This suggests that, as in S. punctatus on Stephens Island, female S.p. punctatus on northern islands do not ovulate each year.

Animals↗
PubMed1994

Substrate and inhibitor specificities of the thermostable alcohol dehydrogenase allozymes ADH-71k and ADH-FCh.D. of Drosophila melanogaster.

Purified thermostable alcohol dehydrogenase allozymes ADH-71k and ADH-FCh.D. of Drosophila melanogaster have been compared with the two common enzyme forms ADH-F and ADH-S. Enzyme kinetic parameters for various primary and secondary alcohols were determined under standard conditions used previously. Both ADH-71k and ADH-FCh.D. show ADH-S-like reaction kinetics and Km values, due to retrograde evolution at site 214, Pro-->Ser. Inhibition studies with alcohol dehydrogenase inhibitors pyrazole, 4-methylpyrazole, and cibacron blue 3GA were also performed. Activity measurements on crude extracts of larvae and flies from isogenic lines of ADH-FCh.D. revealed a consistently higher activity than in ADH-71k-containing strains, in contrast to the original strains.

Alcohol Dehydrogenase↗
PubMed1994

A short-term study of nitrofurantoin prophylaxis in children managed with clean intermittent catheterization.

OBJECTIVE: Because there is no evidence for the effectiveness of antibiotic prophylaxis in children with neurogenic bladder, the value of once-daily nitrofurantoin macrocrystals was assessed in a selected population with neurogenic bladder due to meningomyelocele. METHODS AND TRIAL POPULATION: Children with significant urinary tract abnormalities other than neurogenic bladder were excluded. A urinary tract "infection" was defined as > or = 10(8) colony forming units of bacteria/L of urine together with pyuria of > or = 50 x 10(6) leukocytes/L, and/or symptoms consistent with an urinary tract infection. Fifty-six children participated in a 24-week double-blinded, placebo-controlled cross-over study. The infection status was assessed at two weekly intervals or if relevant clinical manifestations occurred. RESULTS: For the whole trial the average percentage of "infections" per urine sample for each patient was reduced from 39% on placebo to 19% on single daily dose prophylaxis (P < .0003). For the first 12 weeks of the trial corresponding figures were 45% on placebo and 22% on prophylaxis (P < .0018). There was evidence for a marked carryover protective effect of nitrofurantoin into the placebo arm of the trial. CONCLUSION: Nitrofurantoin is an effective prophylactic agent during a 3-month period. Long-term studies are needed to confirm the reasonable expectation of a beneficial effect on urinary tract damage.

Child↗
PubMed1993

Application of a leukocyte and nitrite urine test strip to the management of children with neurogenic bladder.

A urine leukocyte count of > or = 50/mm3 together with a bacterial count of > or = 10(5) colony-forming units (CFUs) per milliliter was used to define significant infection in 160 children with neurogenic bladder and evaluate the leukocyte and nitrite components of the Chemstrip 9 test. A Chemstrip 9 leukocyte reading of < or = 25 together with a negative nitrite reaction occurred in 99 children and had a sensitivity of 83.5% and a negative predictive value for infection of 97.0%. A Chemstrip 9 reading of > or = 500 leukocytes together with a positive nitrite reaction occurred in 18 children and had a sensitivity of 40% with a 100% positive predictive value for infection. Other combinations of Chemstrip 9 leukocyte and nitrite reactions were unhelpful or of uncertain value. Selection of up to three specimens from each patient increased the number of samples to 360 and provided general confirmation of the above conclusions. Nitrofurantoin may reduce the sensitivity of the nitrite strip reaction.

Child↗
PubMed1993

Assessment of DNA fingerprinting for determining genetic diversity in sheep populations.

Genomic DNA, prepared from 12 animals from four sheep flocks, was digested with either HaeIII or HinfI and probed with three DNA fingerprinting probes. Mean DNA fingerprint band sharing and band frequency calculated for each flock were used to estimate genetic diversity. Each of the DNA fingerprinting systems showed the same trend in diversity within the sampled flocks, and greater diversity between the flocks than within the flocks. DNA fingerprinting therefore provides a useful measure of genetic diversity in sheep.

Analysis of Variance↗
PubMed1992

Independent origins of New Zealand moas and kiwis.

Two groups of flightless ratite birds existed in New Zealand during the Pleistocene: the kiwis and the moas. The latter are now extinct but formerly included 11 species. We have enzymatically amplified and sequenced approximately 400 base pairs of the mitochondrial 12S rRNA gene from bones and soft tissue remains of four species of moas as well as eight other species of ratite birds and a tinamou. Contrary to expectation, the phylogenetic analysis shows that the kiwis are more closely related to Australian and African ratities than to the moas. Thus, New Zealand probably was colonized twice by ancestors of ratite birds.

Animals↗
PubMed1991

Three cases of disputed paternity in dogs resolved by the use of DNA fingerprinting.

DNA fingerprinting with the probes 33.15 and alpha-globin 3'HVR has been used to resolve three cases of disputed paternity in dogs. For each pedigree it was necessary to establish which bands in the DNA fingerprints of the offspring were of paternal origin, and then establish which putative sire carried all these bands. In the first case, a litter of Rhodesian Ridgebacks, twelve DNA bands were informative in establishing paternity. In the second case, a litter of Afghan hounds, five DNA bands established paternity, Lastly, in a litter of Border collies, five DNA bands established paternity. In each case a single dog only sired the entire litter.

Journal Article↗
PubMed1990

Absence of daily cycles in plasma sex steroids in male and female tuatara (Sphenodon punctatus), and the effects of acute capture stress on females.

The possible existence of daily cycles in plasma concentrations of sex steroids was examined in wild male and female tuatara (Sphenodon punctatus). Samples were collected from freshly captured animals at dusk, middle of the night, dawn, and middle of the day in January (summer) and July (winter). Males showed daily cycles in mean body temperature (Tb) in both seasons but no daily cycle in mean plasma testosterone concentration in either season. Vitellogenic female tuatara in January and females in mixed reproductive condition in July also showed significant daily variation in Tb. However, there were no daily cycles in mean plasma concentrations of estradiol, testosterone, or progesterone in either group of females. Vitellogenic female tuatara subjected to an acute capture stress (3-hr confinement) in January had mean plasma concentrations of estradiol and testosterone that did not differ from those of free-roaming females. However, progesterone and Tb were significantly higher in captives than in free-roaming females. The elevation in progesterone may result from physical confinement, the difference in Tb, or both. These data suggest that seasonal fluctuations in circulating concentrations of plasma sex steroids in tuatara can be determined using samples collected at different times of the 24-hr cycle. However, the effects of acute capture stress and/or changes in Tb on plasma progesterone concentrations need to be considered in future studies on this and possibly other female reptiles.

Animals↗
PubMed1990

The genetics of human alcohol metabolism.

1. The custom of drinking alcoholic beverages is a human behavior with serious social and medical consequences for a surprisingly large fraction of drinkers. 2. This review describes recent advances in our understanding of the genetic loci that control enzyme systems involved in the metabolism of alcohol. 3. These advances make possible new experimental programs that may lead to simple diagnostic tests for patients at risk of developing alcohol abuse behaviour.

Alcohol Dehydrogenase↗
PubMed1989

Sequence, structure and evolution of the gene coding for sn-glycerol-3-phosphate dehydrogenase in Drosophila melanogaster.

We present the complete nucleotide and deduced amino acid sequence for the gene encoding Drosophila sn-glycerol-3-phosphate dehydrogenase. A transcription unit of 5kb was identified which is composed of eight protein encoding exons. Three classes of transcripts were shown to differ only in the 3'-end and to code for three protein isoforms each with a different C-terminal amino acid sequence. Each transcript is shown to arise through the differential expression of three isotype-specific exons at the 3'-end of the gene by a developmentally regulated process of 3'-end formation and alternate splicing pathways of the pre-mRNA. In contrast, the 5'-end of the gene is simple in structure and each mRNA is transcribed from the same promoter sequence. A comparison of the organization of the Drosophila and murine genes and the primary amino acid sequence between a total of four species indicates that the GPDH gene-enzyme system is highly conserved and is evolving slowly.

Amino Acid Sequence↗
PubMed1987

Macromolecular interaction and the electrophoretic mobility of esterase-5 from Drosophila pseudoobscura.

Esterase-5 is one of the most polymorphic loci in Drosophila pseudoobscura. Some variants reportedly produce a dimeric enzyme, while a few produce a monomeric form. This paper reports the finding that during electrophoresis ESTERASE-5 exists in a dynamic equilibrium between monomers and dimers, an equilibrium that is dependent on the running temperature of the gels. This is shown by a series of analytical electrophoresis experiments in which the apparent molecular weights of several variants are determined at four different temperatures. Increasing temperatures result in a linear decrease in the logarithm of apparent molecular weights. Macromolecular interactions thus are a significant determinant of EST-5 electrophoretic mobility.

Animals↗
PubMed1987

Molecular cloning and characterization of esterase-6, a serine hydrolase of Drosophila.

The Est-6 gene of Drosophila melanogaster was cloned by screening libraries with synthetic oligonucleotides corresponding to tryptic peptides from purified esterase-6 (Est-6) protein. cDNA clones were isolated that hybridized in situ to the site of Est-6 on chromosome 3 at 69A1. Inserts in putative Est-6 cDNA clones were 1.85 kilobases (kb) long, and blot hybridization analysis of electrophoretically fractionated RNA, using a cDNA clone as a probe, revealed two transcripts, of 1.68 and 1.83 kb. The two transcripts showed the same developmental profile as the Est-6 protein. Neither transcript was detected in an Est-6-null line. The cDNA fragment was homologous to a 2.3-kb EcoRI-BamHI fragment in genomic clones, and this region was interrupted by the 8-kb B104 transposable element in the Est-6-null line. Conceptual translation of the cDNA sequence revealed a protein of 548 residues with 19% sequence similarity to acetylcholinesterase from the Torpedo ray.

Amino Acid Sequence↗
PubMed1985

Structural analysis of glycerol-3-phosphate dehydrogenase from several Drosophila species.

This report describes preliminary protein structural studies of glycerol-3-phosphate dehydrogenase (alpha-GPDH) from Drosophila spp. and an important innovative feature of our enzyme purification protocol. The scheme involves the coupling of substrate (alpha-glycerophosphate) elution from CM-Sephadex and cofactor (NADH) elution from Affi-Gel blue resin. Using this method a 32.7% yield and a 111-fold purification were obtained from a D. melanogaster line carrying the alpha-GpdhS allele at the alpha-Gpdh locus. The product obtained from 0 to 3-day-old adult flies was electrophoretically homogeneous and consisted mainly of the adult alpha-GPDH-1 isozyme. The method was used to obtain alpha-GPDH protein from D. melanogaster (two lines), D. hydei, D. immigrans, and D. mercatorum. Peptide mapping revealed structural differences among the enzymes from the different species, and amino acid sequencing showed many similarities between D. melanogaster alpha-GPDH and the rabbit muscle enzyme.

Amino Acid Sequence↗