a1 Medical Research Council External Staff, Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford, OX1 3RE, U.K.
a2 Institut für Genetik, Gesellschaft für Strahlen- und Umweltforschung, D-8042 Neuherberg, F.R.G.
A centromeric heterochromatin (Hc) comparison of two substrains of the mouse inbred strain 101 with another two, revealed differences in at least two and possibly in up to six chromosome pairs. The differences could have arisen by the inclusion of chromosomes from the inbred strain C3H/He.
(Received July 19 1985)