Human Genetics

, Volume 63, Issue 2, pp 171–174

Cytologic evidence for three human X-chromosomal segments escaping inactivation


  • Werner Schempp
    • Institut für Humangenetik und Anthropologie
  • Barbara Meer
    • Institut für Humangenetik und Anthropologie
Original Investigations

DOI: 10.1007/BF00291539

Cite this article as:
Schempp, W. & Meer, B. Hum Genet (1983) 63: 171. doi:10.1007/BF00291539


Early replication of prometaphasic human sex chromosomes was studied with the bromodeoxyuridine (BrdU)-replication technique. The studies reveal that two distal segments of Xp, including bands Xp 22.13 and Xp 22.3, replicate early in S-phase and therefore may not be subject to random inactivation. Furthermore, the replication of these distal segments of Xp occurs synchronously with those of the short arm of the Y chromosome including bands Yp 11.2 and Yp 11.32. These segments of Xp and Yp correspond well to the pairing segment of the X and Y chromosomes where a synaptonemal complex forms at early pachytene of human spermatogenesis. The homologous early replication of Yp and the distal portion of Xp may be interpreted as a remnant left untouched by the differentiation of heteromorphic sex chromosomes from originally homomorphic autosomes. A third early replicating segment is situated on the long arm of the X chromosome and corresponds to band Xq 13.1. This segment may be correlated with the X-inactivation center postulated by Therman et al. (1979).

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© Springer-Verlag 1983