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A survey of mtDNA variation among populations of chum salmon Oncorhynchus keta around the Pacific Rim revealed four large population groups: Rim of the Sea of Japan, the Rim of the Okhotsk Sea and West Bering Sea, North-west Alaska and Gulf of Alaska. The observed population structure appears to reflect isolation by distance with limited gene flow between regions and larger amounts of gene flow between populations within these four regions. [ABSTRACT FROM AUTHOR]

This article focuses on the 20th Wakefield Symposium, "The Genetics of Subpolar Fish and Invertebrates," which is the successor of the 11th Wakefield Symposium. One of the predominant themes of both symposia was the descriptive study of population structure. Descriptive studies are an important step in developing management or conservation plans because they can provide markers for use in stock identification programs and because they can identify distinct productivity units in species that do not have convenient or obvious geographical boundaries, such as many marine species.

A simple gas chromatographic technique for the measurement of 16 alpha-hydroxydehydroepiandrosterone sulphate in urine from pregnant women is described. An assessment was made of the effectiveness of the measurement of this oestriol precursor for the antenatal diagnosis of placental steroid sulphatase deficiency. Twenty-two patients whose pregnancies were complicated by subnormal oestrogen excretion for gestation were studied. In nine of these, where placental steroid sulphatase activity was found subsequently in vitro to be normal, the excretion of 16 alpha-hydroxydehydroepiandrosterone sulphate was less than 27 mumol/24 h. In the remaining 13 patients, in whom postnatal in vitro assay demonstrated absence of placental steroid sulphatase activity, urinary excretion of 16 alpha-hydroxydehydroepiandrosterone sulphate was 59-360 mumol/24 h. The excretion of this metabolite was below the limit of detection (20 mumol/24 h) in 30 uncomplicated pregnancies. It is concluded that urinary excretion of 16 alpha-hydroxydehydroepiandrosterone sulphate greater than 50 mumol/day or a ratio of urinary 16 alpha-hydroxydehydroepiandrosterone sulphate to urinary oestrogen greater than 2.0 correctly identifies, before delivery, those pregnancies in which fetus and placenta are deficient in steroid sulphatase activity.