Chapter 18.12 Structure determination in the presence of twinning by merohedry

Crystallography of biological macromolecules

Second Online Edition (2012)

Part 18. Refinement

  1. T. O. Yeates1,
  2. M. R. Sawaya2

Published Online: 14 APR 2012

DOI: 10.1107/97809553602060000866

International Tables for Crystallography

International Tables for Crystallography

How to Cite

Yeates, T. O. and Sawaya, M. R. 2012. Structure determination in the presence of twinning by merohedry. International Tables for Crystallography. F:18:18.12:548–551.

Author Information

  1. 1

    Department of Chemistry and Biochemistry, University of California, Los Angeles, PO Box 951569, Los Angeles, CA 90095–1569, USA

  2. 2

    Institute for Genomics and Proteomics, UCLA-DOE, 611 Young Drive East, Los Angeles, CA 90095, USA

Publication History

  1. Published Online: 14 APR 2012


This chapter details strategies for determining structures based on intensity data suffering from twinning. Progress can often be made in the early stages of structure determination without taking the twinning into account, whereas proper refinement of structures must account for the effects of twinning. Complications that can occur when handling anomalous-scattering information are discussed. Opportunities are identified for more formal treatments of the problem of phasing twinned data. The facility with which twinning can be analysed and discriminated from local noncrystallographic symmetry during the final stages of analysis is emphasized.


  • twinning;
  • merohedral twinning;
  • structure determination