Statistical analysis of the migration component of genetic drift

Statistical methods are introduced for analysis of the migration component of genetic drift, i.e., of the stochastic changes that affect allele frequencies during migration between local groups. Attention focuses on alpha M, a parameter that measures the extent to which this component of drift departs from the ideal of independent random sampling, and which can be interpreted as a measure of the extent to which migration is kin-structured. It is shown that alpha M can be estimated from genetic data, even in the absence of information about the genealogical relationships of migrants, and Monte-Carlo simulations are used to approximate the sampling distribution of the estimator under the null hypothesis of independent random sampling. Application of these methods to data from the Aland Islands, Finland, shows that the migration pattern there is consistent with the hypothesis of independent random sampling.

Three components of genetic drift in subdivided populations

Wright's metaphor of sampling is extended to consider three components of genetic drift: those occurring before, during, and after migration. To the extent that drift at each stage behaves like an independent random sample, the order of events does not matter. When sampling is not random, the order does matter, and the effect of population size is confounded with that of mobility. The widely cited result that genetic differentiation of local groups depends only on the product of group size and migration rate holds only when nonrandom sampling does not occur prior to migration in the life cycle.

The effect of non-random migration on genetic differences between populations

Models of genetic population structure generally assume that emigrants from each local group are drawn at random from the set of individuals born there. We show that small violations of this assumption can have disproportionately large effects on genetic population structure, and we introduce a statistical method for measuring this effect.

Correlations between relatives in small populations

Correlations between relatives in small, closed populations can be substantially smaller than predicted by the classical formulas of population genetics. This effect is especially pronounced for relatives whose most recent common ancestor is several generations removed. When the effective population size is small, correlations between even close relatives can be negative. This implies that in small populations conventional estimators of quantitative genetics parameters will be biased and that preferential treatment of close relatives will be less likely to evolve.

POPULATION STRUCTURE AND QUANTITATIVE CHARACTERS

A migration matrix model is used to investigate the behavior of neutral polygenic characters in subdivided populations. It is shown that gametic disequilibrium has a large effect on the variance among groups but none at all on its expectation. The variance of among-group variance is substantial and does not depend on the number of loci contributing to variance in the character. It is just as large for polygenic characters as for single loci with the same additive variance. This implies that one polygenic character contains exactly as much information about population relationships as one single-locus marker. The theory is compared with observed differentiation of dermatoglyphic and anthropometric characters among Bougainville islanders.

The determination of diamorphine by thin-layer chromatography and spectrophotometry

THE assay of diamorphine in Diamorphine Injection B.P. is based on its hydrolysis to morphine followed by a colorimetric determination (Allport & Jones, 1942; Stephens, 1951; Hooper, Shaw & Tims, 1967). Stored solutions of diamorphine may contain O3- and O6-acetyl-morphines as well as diamorphine and morphine (Davey, Murray & Rogers, 1967); all are converted into morphine in the first stage of the British Pharmacopoeial assay of the injection and thus contribute to the final morphine content.

Separation of opium alkaloids and their acetylated derivatives by thin-layer chromatography has already been reported (Mary & Brochmann-Hanssen, 1963; Vignoli, Guillot & others, 1965, 1966a, b) and the application of this technique to diamorphine, the acetylmorphines and morphine is discussed below.