Tail Biopsy
MDS offers PCR services to determine if genetically engineered mice carry a gene of interest, tail snips are commonly performed to obtain DNA samples. DNA for PCR analysis can also be obtained from car punches and digits clipped during identification procedures, blood samples or saliva swabs. To obtain larger amounts of DNA for Southern Blot testing, tail biopsy is usually performed. Tail biopsy is safe and humane when it is performed correctly.
Sampling must be performed using sharp, sterile instruments, such as a scalpel blade or scissors. If tail biopsies are performed on multiple mice, instruments must be disinfected in 70% alcohol for at least 15 minutes or sterilized using a hot bead sterilizer prior to being re-used. Please note that disposable scalpel blades are not designed to be used on multiple animals, and a fresh blade must be used for each mouse. The smallest possible section of tail should be removed and adequate hemostasis should be achieved via a styptic (e.g., silver nitrate, cautery, tissue adhesive, etc.). It is recommended that tail samples be limited to no more than 10 mm of tissue.
Tail Biopsy Preparation for Direct DNA Extraction (small volume)
- Pups can be tailed for PCR or Southerns and identified by toe clipping at 10-14 days of age.
- Clip toes according to scheme.
- Clip ~0.5-1cm of tail and place into a clean, labeled, 1.5ml Eppendorf tube.
- Immediately place entire tube on dry ice.
- Tissue can be obtained by ear punching which can also serve as identification
- Small quantities of blood from distal veins(e.g., saphenous vein) may be used for analysis
- PCR analyses using saliva and hair have also been described among others
To ensure the genetic quality and monitor the genetic drift of inbred and transgenic laboratory animals, DNA fingerprinting is available using detection of Restriction Fragment Length Polymorphisms (RFLP5), hybridization patterns, and chromosome mapping; indices of bandsharing, heterozygosity, and genetic distance.
STRAIN CHARACTERIZATION AND DIFFERENTIATION
To compare/contrast the genetic relatedness of inbred strains and to determine the presence or absence of a gene (in transgenics or knock-outs), DNA bands are compared. Homozygous animals of different strains will exhibit unique bands; heterozygotes will carry bands from both parent strains.
PATERNITY DETERMINATION
DNA-based testing is performed by compare genetic profiles of the dam, offspring, and possible sires. Since the offspring inherits half the DNA pattern from each parent, eliminating the DNA known to be from the dam and comparison of remaining DNA with that of all possible sires allows almost certain identification of the actual sire. This method requires only a few drops of blood, a small piece of tissue (such as the tip of a tail or tissue from ear punch), or a swab of the mouth.