Extraction
DNA can be successfully recovered from a wide range of tissues. However, factors such as freshness, method of preservation, and age of the preserved specimen all have an impact on the overall success of obtaining a DNA sequence. These factors may influence i) the integrity of DNA within the specimen, as well as ii) the method of extraction.
Fresh, un preserved tissue is ideal when conditions permit. However, many 'wet' tissues degrade rapidly once cell death occurs. Cell lysis and the release of enzymes can quickly destroy the DNA content of a sample. A general rule of thumb when using fresh material is 'the fresher, the better'!
Some common methods of preservation include flash-freezing, ethanol, dessication, and formalin. Flash-freezing from fresh tissue is a very effective means of preservation, and extraction results are typically comparable to using fresh tissue directly. Simple methods, such as a proteinase K digestion are usually sufficient. Ethanol is also a reliable method, where DNA may be readily recovered from specimens up to 10 years old using simple extraction techniques.
Dessicated or dried samples are often encountered when dealing with museum specimens. In some cases, simple methods may suffice, but more involved techniques may also be required (particularly with older samples). Formalin is another method common in older collections and presents a formidable challenge for DNA recovery. However, some protocols have been developed which have yielded modest amounts of DNA from formalinized tissue.
