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Rodent Genotyping

Genetic identification of research rodents is often accomplished through the use of PCR analysis of DNA extracted from tail or ear punch tissue. DNA may also be obtained from other samples, such as hair, blood and oral swabs.

Deviations from PSU IACUC genotyping guidelines must be described in the PI's IACUC protocol. Personnel must receive sufficient training to perform the procedures in a safe and humane manner.

Guidelines for tissue collection


Ear punch/ear snip: Tissue for genotyping may be collected by ear punch or snip at any age and does not require anesthesia. This is the preferred method of tissue collection for genotyping of rodents.

Ear punch - The amount of tissue collected from a 1-2 mm sterile ear punch is usually adequate for genotyping and may be performed on any age mouse without general anesthesia. Ear punches must be cleaned and disinfected between animals.

Ear snip - Using a sharp, sterile scissors, 2-3 mm may be snipped from the tip of the ear to collect tissue for genotyping. Scissor tips must be cleaned and disinfected between animals. This procedure may be performed on any age mouse without general anesthesia.

Tail Tip Amputation: Animals must be less than 3 1/2 weeks of age at the time of tail tip amputation for genotyping. DNA yield from tail tissue has been shown to be highest in 10-21 day old rodents. Tail tissue analysis and identification of desired mice prior to weaning may allow more efficient use of resources. In addition, cutting through the soft tissue in the tail of a young mouse is likely to be less painful than cutting through more extensively mineralized bone and mature tissue in older animals. Tail tip collection should be perform ed at as young an age as feasible.

    • Animals less than 3.5 weeks of age: Collection of tail tissue may be performed without general anesthesia. Local anesthetic methods are available. Please contact an ARP veterinarian for more information.
    • Animals greater than 3.5 weeks of age: Samples for genotyping must be collected by ear punch or ear snip.

In most cases, 2 mm removed from the tip of the tail is adequate for genotyping. No more than 5 mm of tissue may be removed from an animal. DNA yield does not proportionally increase as larger amounts of tail tissue are collected. Tail amputation should be done using a sharp, sterile scissors that is cleaned and disinfected between animals. Note: all tissue must be removed from the scissors after each animal for accurate DNA analysis via PCR.

Blood loss should be minimal from animals less than 3.5 weeks of age when proper procedures are used. If needed, bleeding may be controlled by applying direct pressure to the tip of the tail. Styptic powder/pencils and silver nitrate are chemical cauterizing agents that may be used if necessary. Use of heat to cauterize the tail end is not allowed.

Special circumstances: If it is necessary to collect a second sample from an animal, the sample must be collected via ear punch or ear snip.

More information on collecting tissue for genotyping may be found on the NIH Office of Intramural Research website.