MAPPING STUDIES OF THE DISTAL IMPRINTING REGION OF MOUSE CHROMOSOME-2

The known limits of the distal imprinting region of mouse Chromosome ( Chr) 2 are defined by the breakpoints of the translocations T(2; 8)2Wa , (T2Wa), and T(2; 16)28H, (T28H), in distal H3, and proximal H4 respe ctively. We have shown that T2Wa and T(2;4)1Go, (T1Go), which has a br eakpoint in central H3 map close to a, non-agouti. Ada, adenosine deam inase, lies very near the proximal boundary and Ra, ragged, maps very close to the distal boundary, and is less than 0.2 cM from wasted, wst . From the current data Ada can be taken as the proximal, and Ra as th e distal gene marker of the imprinting region on the linkage map. From consensus maps twenty three other markers, including fourteen genes, lie between Ada and Ra, some of which may be useful in investigations of imprinting. Of the markers included in the study reported here, fou r, Ada, ls, lethal spotting, Ra and wst lie or probably lie within the region but none display any evidence of imprinting. We suggest that r ecombination frequency is elevated in distal Chr 2, because in none of the crosses could the most closely linked marker be ordered in relati on to the translocation breakpoint due to the high frequency of double crossovers.