Supergenes in polymorphic land snails. I. Partula taeniata

The general colour of the shell in Partula taeniata is controlled by at least two loci. One of these (C) has a series of six alleles which determine the yellow (Y) and neutral brown (N) series of colours. Alleles for darker colours are dominant to those for lighter colours, but dominance is not always complete. The pink (P) colours are determined by a second locus (P) which modified the expression of the lighter alleles of the C locus. Orangeshell colour segregates with yellow but its allelic relationship is unknown. Colour of the lip is controlled by a locus (L) with pink lip dominant to white lip. The colour of the spire is determined by a locus (S) with dark (N4) spire dominant to light spire. An intermediate spire colour shows the same pattern of inheritance and may represent the effect of another allele. Banding of the shell is dominant to absence of bands, with two loci (B1 and B2) determining the type of banding. An allele at B1 produces the frenata pattern; an allele at B2 produces zonata; together they produce lyra. All the loci for which linkage data are available are linked so strongly that the whole array may be considered a supergene. Self-fertilisation takes place primarily during early reproductive life. About 20 per cent of the young of the first mating of an individual are produced by selfing, but over the whole reproductive span the frequency is only about 2-5 per cent. There is inconclusive evidence for heterozygote advantage of banded individuals.

Effects of radial artery cannulation

A prospective study has been carried out in 40 patients of the effects of radial artery cannulation for monitoring purposes. A Doppler flow meter was used to secure objective evidence of the incidence of thrombosis in the cannulated radial artery. Twenty-two of the 41 arteries cannulated were shown to have undergone thrombosis, and the haemodynamic defect associated with the arterial block persisted in all but two until the time of the patient's discharge from hospital. Thirteen of the 20 hands in which a persistent block was demonstrated developed features of mild ischaemia. In four instances, these were transient, and disappeared within a few days. In the remaining nine hands, however, the features persisted to the time of the patient's discharge from hospital at an average of three weeks from the date of cannulation. The mean cannulation time was 45 hours. Radial artery cannulation carries a definite morbidity, and should not be used unless there is no other reasonable way of obtaining vital information for the management of a critically ill patient.

The contribution of ecological genetics to evolutionary theory: detecting the direct effects of natural selection on particular polymorphic loci

It is possible to define a strategy for experimentally demonstrating that natural selection acts directly on a particular polymorphic locus, rather than on other loci in linkage disequilibrium with it. This strategy has been applied to the alcohol dehydrogenase polymorphism of Drosophila melanogaster and has provided very strong evidence that the polymorphism is directly subject to selection. It is equally applicable to other polymorphisms and offers the hope of resolving the long-standing debate about the causes of enzyme variation.

Oxygen administration during artifical ventilation with pressure cycled respirators

Inspired oxygen concentration has been measured when ventilating lung models and patients with Bird pressure cycled respirators. It has been found that with normal lungs the inspired oxygen concentration is predictable from the end-inspiratory pressure recorded on the respirator manometer. When lung mechanics are abnormal, the relationship between inspired oxygen concentration and end-inspiratory pressure is not sufficiently precise to allow accurate prediction of inspired concentration of oxygen.