Genetic Assays to Study Repeat Fragility in Saccharomyces cerevisiae

  • Erica J. Polleys
  • Catherine H. FreudenreichEmail author
Part of the Methods in Molecular Biology book series (MIMB, volume 2056)


Trinucleotide repeats are common in the human genome and can undergo changes in repeat number and cause length-dependent chromosome fragility. Expanded CAG repeats have been linked to over 14 human diseases and are considered hotspots for breakage and genomic rearrangement. Here we describe two Saccharomyces cerevisiae based assays that evaluate the rate of chromosome breakage that occurs within a repeat tract (fragility), with variations that allow the role of transcription to be evaluated. The first fragility assay utilizes end-loss and subsequent telomere addition as the main mode of repair of a yeast artificial chromosome (YAC). The second fragility assay relies on the fact that a chromosomal break stimulates recombination-mediated repair. A PCR-based assay can be used to evaluate instability of the repeat in the same conditions used to measure repeat fragility. These assays have contributed to understanding the genetic mechanisms that cause chromosome breaks and tract-length changes at unstable trinucleotide repeats.


Chromosome breakage Fragility Repeat instability Yeast artificial chromosome (YAC) Direct duplication recombination assay (DDRA) 



Work in our laboratory is currently supported by grants from the National Institute of Health (GM105473, GM122880) and National Science Foundation (MCB 1817499). We would like to thank past and present members of the C. H. Freudenreich and V.A. Zakian labs for their contributions to the development of these assays.


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© Springer Science+Business Media, LLC, part of Springer Nature 2020

Authors and Affiliations

  1. 1.Department of BiologyTufts UniversityMedfordUSA

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