The capacity of the fourth chromosome of Drosophila melanogaster to establish end-to-end contacts with the other chromosomes in salivary-gland cells

When the fourth chromosome of Drosophila melanogaster is attached, as the result of an induced translocation, to 21A in 2L or 60E in 2R, its tip exhibits a marked capacity to pair end-to-end with the tips of the other chromosomes. In each of the translocations, about 59 per cent of the contacts involving the tip of 4 were with the tip of X. If this pairing preference reflects structural similarity, the tip of 4 is much more like the tip of X than that of any other chromosome. The significance of this phenomenon is discussed with respect to the standard pattern of end-to-end association in the Oregon-R wild-type stock that provided the control preparations. In the 4-2L rearrangement, the interaction of chromosome 4 with the tip of 2L (101E with 21A) led to pronounced puffing in subdivisions 21A and B, as was most strikingly manifested when the distal segments of 2L failed to synapse and the homologue of paternal origin showed a large puff whereas that of maternal origin (not carrying the fourth chromosome) remained unpuffed.This study was supported in part by a Research Grant (GM-10499) from the National Institutes of Health, U.S. Public Health Service.