UNIT 8.6 Analysis of Sister-Chromatid Exchanges

  1. James German,
  2. Becky Alhadeff

Published Online: 1 MAY 2001

DOI: 10.1002/0471142905.hg0806s02

Current Protocols in Human Genetics

Current Protocols in Human Genetics

How to Cite

German, J. and Alhadeff, B. 2001. Analysis of Sister-Chromatid Exchanges. Current Protocols in Human Genetics. 2:8.6:8.6.1–8.6.10.

Author Information

  1. New York Blood Center, New York, New York

Publication History

  1. Published Online: 1 MAY 2001
  2. Published Print: AUG 1994


Two requirements for the cytogenetic analysis of sister-chromatid exchanges (SCEs) in somatic cells are (1) a population of actively proliferating cells that will provide an adequate number of metaphases and (2) sister chromatids that in some way are differentially labeled or stained in the metaphases. SCEs can be recognized as abrupt discontinuities in the staining patterns of the two chromatids of a metaphase chromosome at what appear to be identical sites, with reciprocal switching from one chromatid to its sister. This protocol uses phytohemagglutinin (PHA)-stimulated cultures of blood lymphocytes as a source of proliferating cells. The cells are incubated with the thymidine analog BrdU. Slides prepared from fixed cells with BrdU-substituted chromosomes are treated with Hoechst 33258, exposed to light and heat, and then Giemsa-stained to produce differentially stained chromosomes. The chromatids with bifilar substitution exhibit a lighter purple stain than their unifilarly substituted sister chromatids.