| Success Rates for DNA Extraction from | | | | rain). |
| Non-Standard Samples | | | | Low (20% - 30%) For samples such as |
| In part 1 of the article, we looked at | | | | teeth or bone, where extracting DNA is a |
| some of the more common non-standard | | | | relatively difficult and time consuming |
| samples used to obtain DNA from an | | | | process, these normally need to be |
| individual for DNA testing purposes. In | | | | handled by a highly specialised |
| this article we look at DNA extraction | | | | laboratory. In such cases, the |
| success rates from the various types of | | | | individual should consult the laboratory |
| samples and how these can vary from one | | | | first to check their level of expertise, |
| sample to another. | | | | if they will accept the sample and the |
| Non standard samples do not always | | | | cost. |
| guarantee that a DNA Profile will be | | | | The classification above is however only |
| obtained. Whilst for buccal swabs it is | | | | a guideline, since as we have seen it is |
| possible not to obtain DNA, such as in | | | | not just the type of sample that is |
| cases where the swabbing was not | | | | important but also other variables can |
| adequately performed or else the swabs | | | | have an influence such as : |
| grows mould due to damp storage | | | | 1. Poor storage conditions (e.g. damp |
| conditions, in general problems with | | | | environment, extreme heat etc) |
| this type of sample are normally less | | | | 2. Poor sample handling (possible |
| than 2%. Therefore depending on the | | | | contamination with other DNA or dirt by |
| nature of the sample, there is usually | | | | touching the sample) |
| associated a High, Medium or Low | | | | 3. Not enough DNA present (e.g. heavily |
| probability of success in extracting DNA | | | | used toothbrush vs used once only) |
| from each type of sample (in some cases | | | | It is also important to note that the |
| a percentage probability of success is | | | | success rate will also depend heavily on |
| provided). | | | | the ability of the laboratory performing |
| High (80%) : For samples such as fresh | | | | the test. Not all laboratories that can |
| blood stains or hairs with root where, | | | | perform DNA Paternity testing on normal |
| for a qualified and experienced DNA | | | | swabs are capable of obtaining DNA from |
| laboratory, extracting DNA is considered | | | | a wide variety of other media. The more |
| relatively straightforward. In such | | | | difficult the media (e.g. teeth and |
| cases, as long as the sample is handled | | | | bone), the greater the specialisation |
| properly both during collection and | | | | and experience required to increase the |
| delivery to the laboratory, one can | | | | chance of a successful DNA extraction. |
| expect a high probability of success in | | | | Finally, it is also important to note |
| extracting DNA. | | | | that with non-standard samples there is |
| Medium (50%-60%) : For samples such as a | | | | always a risk that the extraction will |
| toothbrush or cigarette butts the | | | | not work. Therefore any person |
| success rate is influenced by a number | | | | considering submitting such a sample, |
| of variables including heavy use vs | | | | especially where it may be only a |
| light use and/or storage conditions etc. | | | | limited sample available (e.g. person is |
| Therefore a heavily smoked cigarette | | | | dead), should take this into |
| butt found in an ashtray at home is more | | | | consideration. Selection of an |
| likely to result in a successful DNA | | | | experienced laboratory (possibly of |
| extraction than a lightly smoked | | | | forensic specialization) will help |
| cigarette that has been thrown on the | | | | minimize this risk. |
| street and exposed to the elements (e.g. | | | | |