Blood group incompatibility between mother and foetus.

Genetic studies in the Lepidoptera Many of you will know that my interest in human genetics derived from breeding butterflies, and it was the phenomenon of mimicry in these insects which caused my colleague P. M. Sheppard and myself to become interested in the Rhesus blood groups, and through them in the general subject of blood group incompatibility between mother and foetus. Because the connection between the butterflies and the blood groups may not be clear to you, I felt that we should spend a few minutes with the Lepidoptera so that I can explain. Plate 1 shows three butterflies. The first (a) Parides coon (Fabricius) is known as a model because it is imitated. It is a distasteful insect, its body containing digoxin-like alkaloids, and because of this predators (usually birds) having sampled it once leave it alone subsequently. The second butterfly (b) Papilio memnon L. f. achates is a mimic, having evolved a wing pattern strongly resembling the model. It is edible, and the resemblance is a very powerful protective mechanism. The most important rule governing mimicry contradicts the view that nothing succeeds like success for, as the mimics increase in number relative to the models, they become more and more at risk, the birds coming to associate their pattern not with inedibility but with edibility. So it pays a mimic to be rare, but as there is danger then of extinction this type of mimicry favours polymorphism as a means of maintaining a large population, and one mimetic species will imitate many different models in the same area. The third insect (c) is a male. Though it is not mimetic it carries the genes controlling the mimetic pattern, these being autosomal and sex-limited to the female. Plate 2 exemplifies polymorphism in P. memnon, f. agenor (a) being quite distinct from f. achates (b). Breeding experiments show that what appears to be a single gene converts one into the other, but this view has to be modified because in the same sibship very occasionally a third form, f. titania (c) has appeared. F. titania has some of the characteristics of achates (the small white patch on the hindwing and the long tails) but the black body of agenor. Correspondence: Professor C. A. Clarke, Department of Medicine, The University of Liverpool, Ashton Street, P.O. Box 147, Liverpool L69 3BX.