Relationship between genetic and physical distance across the length of human chromosome 7. This relationship was examined for the mapped Genethon genetic markers with interlocus Kosambi map distances in cM (see Fig. 2). For physical distances, the computed versions of the anchored contigs listed in Table 1 were placed end-to-end in their established order and orientation (when known), assuming a distance of zero between contigs. The unanchored contigs were not included in the analysis. The intervening physical distance between successive Genethon genetic markers was then measured, ignoring markers at discrepant relative positions on the genetic and physical maps. The terminal segments, between the telomeres and the first or last Genethon genetic markers, were not considered. The ratio of genetic distance (in cM) to physical distance (in Mb) was then calculated in overlapping windows of 20 consecutive markers (A. Lynn and A. Chakravarti, unpubl.). The resulting values are plotted against the physical map in a 7p–7q direction, in each case at the mid-point of the physical map interval. Note that the centromere is located roughly at the 60-Mb position on the graph.