Abstract
The replication patterns of human chromosomes can be visualised using the RBG technique. Five to six hours prior to termination of lymphocyte culture, BudR is added to a concentration of 75 mcg/ml. Prepared slides are exposed to 33258 Hoechst and sunlight concurrently, and subsequently stained with Giemsa. The BudR-incorporated (late replicating) regions are stained pale, and the resultant pattern is similar to R-banding. We have been examining the fine details of X chromosome replication in subjects with structural or numerical X abnormalities. In early metaphase cells of children with multiple X chromosomes the late-replicating X's do not replicate synchronously. The degree of asynchrony varies from cell to cell. However, the late-replicating X chromosomes follow a single sequence of replication. Xp22, p11, and q13 replicate first (98%), followed by q26 (95%), q24 and q28 (80%), and q22 (60%). (Percentage indicates the probability of replication prior to addition of BudR). The late replicating major bands are q12 (10%), q23 and q27 (5%), q25 (2%), q21 and p21 (0%). Late replicating sub-bands are seen in p22 (60% of X's), p11 (30% of X's), and q13 (10% of X's). Very early metaphase chromosomes are still under examination and are likely to reveal other late-replicating sub-bands. Exceptions to the above sequence of replication include late replication of Xq13 (4% of X's) and fusion of q22, q24, or q26 possibly due to early replication of q23 or q25 (7% of X's).
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Van Dyke, D., Weiss, L. & Poel, W. 568 PATTERN AND ASYNCHRONY OF LATE X REPLICATION IN CASES OF MULTIPLE X. Pediatr Res 12 (Suppl 4), 458 (1978). https://doi.org/10.1203/00006450-197804001-00573
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DOI: https://doi.org/10.1203/00006450-197804001-00573