Rodent Genotyping

Rodent Genotyping

Approved July 18, 2013   (Download) 


It is often necessary for researchers to genotype the offspring of genetically modified mice.  This is most commonly accomplished by obtaining tissue samples from which DNA is isolated and analyzed (e.g., by PCR, Southern blot analysis).  The most common tissue sampling methods used in mice are tail biopsy and ear punch biopsy.  Less commonly used methods for genotyping mice involve blood sampling and oral swabs to collect cells from the buccal mucosa.
Tail biopsy, or “tailing,” involves cutting a piece of tissue from the terminal end of the tail.  This procedure is often performed without anesthesia when less than 3 mm of tissue is removed.   This works well particularly in young mice (< 28 d), where anesthetic risk is higher and pain appears to be minimal.  Tailing older animals may be painful and is associated with a higher risk of complications.  Researchers are encouraged to consider less invasive alternative methods to tailing when possible, e.g., ear punch biopsy.  Another advantage of ear biopsy over tail biopsy is that both identification and genotyping can be combined in a single event.



Tailing of mice is permitted if IACUC approval is obtained  and the following guidelines are followed  (or strong scientific justification is provided for deviation from the guidelines):

    • Tailing of mice < 28 days of age may be performed without anesthesia or analgesia provided that no more than 3 millimeters of tissue is removed.  Larger samples need scientific justification.
    • Tailing mice > 28 days of age or removal of more than 3 mm of tissue must be performed under appropriate anesthesia (e.g., ketamine/xylazine, isoflurane, etc.) and a minimum of one dose of a systemic analgesic (e.g., buprenorphine, meloxicam, ketoprofen, carprofen) must be administered.
    • If required, mice may be tailed a second time but not at an interval of less than one week from the first biopsy and anesthesia and analgesia must be used regardless of the age of the mice.
    • Researchers should be prepared to control bleeding as necessary following tail biopsy.  Direct pressure is often adequate for small tail biopsies in weanling mice.  For older animals often other methods (e.g., cautery) may be necessary to achieve hemostasis.
    • Instruments used for tailing must be well-maintained such that they are clean and sharp.
  • Ear biopsy:  Anesthesia and analgesia are not required for the collection of small (e.g., 2 mm) ear punch samples in mice.  In mice, the ear is usually sufficiently developed for ear punch biopsy after approximately 4 days of age.


Bonaparte, D. et al., 2013.  FELASA Guidelines for the refinement of methods for genotyping genetically-modified rodents:  a report of the Federation of European Laboratory Animal Science Associations Working Group.  Laboratory Animals 2013:1-10.
Hankenson, C. et al.  2008.  Evaluation of tail biopsy collection in laboratory mice (Mus musculus):  vertebral ossification, DNA quantity, and acute behavioral responses.  JAALAS 47(6):10-18.
Hankenson, C., Braden-Weiss G.C and J. Blendy.  2011.  Behavioral and activity assessment of laboratory mice (Mus musculus) after tail biopsy under isoflurane anesthesia.  JAALAS 50(5):686-694.
Jones, C.P., Carver, S. and L.V. Kendall.  2012.  Evaluation of common anesthetic and analgesic techniques for tail biopsy in mice.  JAALAS 51(6):808-814.