a1 Laboratoire* de Génétique des Populations, Universités Paris 6 et Paris 7, Tour 42, 2 place Jussieu, 75005 PARIS
We analyse the progression of linkage disequilibrium produced by random genetic drift in populations subject to cyclical fluctuations in size. Our model is applied to natural populations of Drosophila which show an annual demographic cycle of bottleneck (finite size) and demographic burst (size supposed to be infinite). In these populations, linkage disequilibrium stabilizes in such a way that, at equilibrium, the expected square of the correlation of gene frequencies E(r2) shows a stable cycle from year to year. If two loci are tightly linked, E(r2) barely varies during the annual cycle. Its values remain close to the value expected in a population of the same but constant effective size. If two loci are loosely linked, fluctuations in E(r2) are large. The maximum value, reached at the end of the bottleneck, is 10 to 100 times greater than the value obtained at the end of the burst. Our results show that the interpretation of observed linkage disequilibrium, by means of statistical tests, requires an accurate knowledge of population demography.
(Received February 04 1986)
(Revised July 08 1986)
* UA CNRS 693. Requests for reprints should be made to C. Montchamp-Moreau.