A.J. Boyce

Population bottlenecks in Polynesia revealed by minisatellites

SummaryTandem-repetitive highly variable loci in the human genome (minisatellites) have been used in gene mapping and as DNA “fingerprints”, but they have not yet found much application in population genetics. We have investigated the capacity of six minisatellites to discriminate between four populations in Oceania. We find that in comparison to Melanesians, Polynesians have a significant loss of heterozygosity (or gene diversity), not noted using more traditional markers. We show also that the number of alleles, the allele distribution and the mutation rates at the Polynesian minisatellite loci do not deviate from those predicted by the neutral mutation/infinite allele model. The low gene diversity is therefore likely to be a result of the maintenance of small population sizes and bottleneck effects during the colonization of the Pacific.

Why are some genetic diseases common

Various processes (selection, mutation, migration and genetic dirft) are known to determine the frequency of genetic disease in human populations, but so far it has proved almost impossible to decide to what extent each is responsible for the presence of a particular genetic disease. The techniques of gene and haplotype analysis offer new hope in addressing this issue, and we review relevant studies of three haemoglobinopathies: sickle cell anaemia, and α and β thalassaemia. We show how for each disease it is possible to recognize a pattern of regionally specific mutations, found in association with one or a few haplotypes, that is best explained as the result of selection; other patterns are due to population migration and genetic drift. However, we caution that such conclusions can be drawn in special circumstances only. In the case of the haemoglobinopathies it is possible because a selective agent (malaria) was already suspected, and the investigations could be carried out in relatively genetically homogenous populations whose migratory histories are known. Moreover, some data reviewed here suggest that gene conversion and the haplotype composition of a population may affect the frequency of a mutation, making interpretation of gene frequencies difficult on the basis of standard population genetics theory. Hence attempts to use the same approaches with other genetic diseases are likely to be frustrated by a lack of suitably untrammelled populations and by difficulties accounting for poorly understood genetic processes. We conclude that although this combination of molecular and population genetics is successful when applied to the study of haemoglobinopathies, it may not be so easy to apply it to the study of other genetic diseases.

Minisatellite mutational processes reduce F st estimates

Abstract. We have used a new method for binning minisatellite alleles (semi-automated allele aggregation) and report the extent of population diversity detectable by eleven minisatellite loci in 2689 individuals from 19 human populations distributed widely throughout the world. Whereas population relationships are consistent with those found in other studies, our estimate of genetic differentiation (Fst) between populations is less than 8%, which is lower than comparative estimates of between 10%–15% obtained by using other sources of polymorphism data. We infer that mutational processes are involved in reducing Fst estimates from minisatellite data because, first, the lowest Fst estimates are found at loci showing autocorrelated frequencies among alleles of similar size and, second, Fst declines with heterozygosity but by more than predicted assuming simple models of mutation. These conclusions are consistent with the view that minisatellites are subject to selective or mutational constraints in addition to those expected under simple stepwise mutation models.

Associations between anthropometric variables and reproductive performance in a Papua New Guinea highland population

Associations between anthropometric variation and reproductive performance have important ecological and evolutionary implications. Bivariate associations between measures of reproductive performance (live births and offspring still living at the time of interview) and 24 anthropometric variables were examined in 150 females, aged 21-44 years, from the Eastern Highlands district of Papua New Guinea. Where significant linear or curvilinear associations with age existed, the reproductive and anthropometric variables were age-corrected. Linear, quadratic and cubic regressions were computed for each bivariate regression of age-corrected reproductive variable on age-corrected anthropometric trait. Positive linear regressions were found in the cases of body weight, triceps skinfold and head breadth. Positive cubic regressions were found in the cases of upper arm circumference, calf circumference, bicondylar femur and wrist breadth. It is suggested that these associations may reflect important ecological factors which influence both anthropometric and reproductive variation. U-shaped associations were found in the cases of wrist breadth and bicondylar femur. Inverted U-shaped associations were found for stature, sitting height, bizygomatic diameter and morphological face height. These curvilinear associations may be interpreted in terms of natural selection, and suggest that stature and sitting height may be undergoing stabilizing selection in this population.

Body composition changes during lactation in a New Guinea population

Some body composition changes during lactation in women of Karkar Island, Papua New Guinea, suggest that body fat reserves, measured by changes in weight, diminish during the course of lactation and that subcutaneous fat reserves diminish with parity. The data are discussed in terms of the possible nutritional control of fertility of women in a subsistence economy.

Migration and Genetic Diversity in an Island Population: Karkar, Papua New Guinea

This paper examines genetic diversity on Karkar Island, Papna New Guinea, and its relation to patterns of migration within and between the two linguistic groups (Waskia and Takia) on the island. Exchange between linguistic groups is found to be small: less than 3 % of married individuals living in one linguistic group were born in the other. There is evidence of a secular trend in movement with significantly greater proportions of younger married individuals living outside their village group of birth. The migration patterns are examined by principal coordinate analysis of kinship coefficients derived from three sets of migration probabilities: ages 15—29, 30—44, 45 and over. For all three age groups the linguistic division is preserved and there is broad agreement between relatedness and the geographical arrangement of the village groups. The 22 polymorphic genetic systems examined show considerable diversity, most of which is within or between village groups in the same linguistic division. The greater level of diversity between Takia groups is consistent with their greater isolation from one another. Genetic distances between village groups show good agreement with geographical distances and there is no overlap between Waskia and Takia. The present-day genetic structure of Karkar Island can be interpreted as being largely the result of the interplay of migration and drift processes. The paper considers the use of analyses of this kind in establishing the magnitude and role of evolutionary forces operating on the genetic structure of human populations and the problems of unravelling rigorously and in detail the historical development of this structure.

Variation in blood pressure in a New Guinea population

The contributions of age and anthropometric, biochemical and socio-economic variables to blood pressure variation in the population of Karkar Island, Papua New Guinea are examined. Blood pressure does not change with age in males; in females there is a decline from ages 21 to 40 and an increase (in systolic pressure) thereafter. Body weight and skinfold thicknesses decline with age in females; arm circumferences decline in both sexes. There were no age effects on serum cholesterol or serum sodium. Variation in ponderal index and subcutaneous fat contribute to variation in blood pressure. The correlations of blood pressure with physique are more important in males and the particular variables concerned suggest a nutritional basis. The socio-economic variables examined showed little variation and this was not associated with variation in blood pressure.

Demographic reductions and genetic bottlenecks in humans : minisatellite allele distributions in Oceania

Polynesians have lower heterozygosities at minisatellite VNTR (Variable Number of Tandem Repeat) loci than have Melanesians; this has been taken as evidence of population-size bottlenecks during the colonisation of Polynesia. We have analysed the allelic distribution of several minisatellite loci in the population of Rapa, a Polynesian island that is known to have undergone a demographic reduction of approximately 95% since first contact with European explorers 200 years ago, leaving a surviving population of 120. We found that the minisatellite diversity of this population does not differ significantly from that of other Polynesian populations, and appears consistent with the neutral expectation of diversity assuming the infinite alleles model. This suggests that the demographic crisis that Rapa underwent did not perturb the allele distribution to the extent that the tests used here could detect. Thus we cannot say that a demographic change of this magnitude constitutes a genetic bottleneck detectable at these loci. The reduced diversity seen in Polynesia must therefore be explained either by more severe bottlenecks as might be expected during colonisation, or else by other causes.

Associations between polymorphic variety and disease susceptibility in two New Guinea populations

During the Australian/British IBP studies on KarKar Island and at Lufa in the Eastern Highlands, Papua New Guinea, information was collected on the epidemiology and genetic constitution of the same subjects. Advantage of this special situation has been taken to determine whether any associations exist between the genetic markers and the disease states. Those found and which appear real include Rhesus D(u) with proteinuria; MN with splenomegaly and hepatomegaly; Ss with parotid enlargement; acid phosphatase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogense and haemoglobin J- Tongariki with presence of malarial parasites; phosphoglucomutase with proteinuria and parotid enlargement; haptoglobin with proteinuria and with splenomegaly and hepatomegaly. These associations are discussed in terms of the probabilities of their arising from heterogeneity in population structure, linkage disequilibrium and pleiotropy.

Evidence for an association between AB0 blood group and goitre

SummaryA medical and genetic study on KarKar Island, Papua New Guinea revealed a significant association between AB0 blood group status and susceptibility to goitre with 0 individuals more susceptible than non-0. The association is found in a number of separate villages on the island which indicates that it is not due simply to chance concordance in geographical patterns of genetic and disease variation.