Identification of Transgenic Animals - Transgenic individuals are the most easily identified when the transgene produces a distinct phenotypic effect, but such cases are only occasional. A more general approach utilizes either dot-blot technique (Appendix 2.I1I) or PCR amplification using genomic DNAs extracted from tail biopsies from 6-7 week old mice.

In case of fish, genomic DNA is usually extracted from pectoral fin tissue. PCR amplification can be used if the trans gene has unique sequences, not found in the host genome, that can be used as primers. This allows very small amounts of DNA from presumptive transgenic individuals to be suitably amplified for a reliable detection of the trans gene.

The samples that test positive for hybridization with the probe are from putative or suspected transgenic individuals. It should be kept in mind that both dot blot and PCR techniques detect the transgene irrespective of whether it is integrated in the genome or is present in an extrachromosomal state.

Therefore, dot blot or PCR assay positive individuals are subjected to Southern hybridization, for confirmation of transgene integration, etc.