title: Kinetics of DNA replication in a dicentric X chromosome formed by long arm to long arm fusion.
abstract: Utilizing the 5-bromo-deoxyuridine (BrdU) incorporation technique, we have recently studied the DNA replication kinetics in a dicentric X chromosome, formed by long arm-to-long arm fusion at band q23, for a 16-year-old black female with primary amenorrhea. The patient has a karyotype 45,X/46,X,dic(X)(q23). In the buccal smear the presence of X chromatin was found in 33% of the cells examined. The Barr bodies are large and 21% of them are bipartite. DNA replication studies were performed on the patient's lymphocytes by the thymidine pulse (T-pulse) method and confirmed comparatively by the BrdU pulse (B-pulse) method. The results indicate that the dicentric X chromosome is always late-replicating. The replication pattern is symmetric on both sides of the breakpoint and the replication sequence is, in order, p11, p22, q1(1-3), q22, q23, p21, and q21. This finding is comparable to those of other investigators and supports the theory that there exist two inactivation centers in the dicentric X chromosome, located on or near the q21 band.
mesh_terms: D000568:Amenorrhea / Q000235:genetics; D001973:Bromodeoxyuridine; D002478:Cells, Cultured; D004261:DNA Replication; D005260:Female; D006801:Humans; D007700:Kinetics; D008214:Lymphocytes / Q000648:ultrastructure; D009030:Mosaicism; D012728:Sex Chromatin / Q000648:ultrastructure; D012729:Sex Chromosome Aberrations / Q000235:genetics*; D012730:Sex Chromosomes; D014960:X Chromosome
chemical_list: D001973:Bromodeoxyuridine