Dna Paternity Testing: Submitting Non-standard Samples (part 1)

DNA Paternity testing is the most accurate way of confirming biological relationships between individuals. The standard way of collecting samples from the individuals to be tested is through the use of oral/buccal swabs. Buccal swabs are relatively easy to use and pain-free since the procedure involves simply rubbing the swab on the inside of the mouth to collect a saliva sample. In addition, they can be easily sent by post to the client when they order a test. Hence, they provide an excellent medium to obtain DNA from an individual.

However, occasions arise when it is not possible to obtain the sample directly from the individual, as for example in the case of a dead or missing person or samples collected from a crime scene. Therefore, in such cases, it is possible to utilise alternative samples (defined as non-standard samples), to obtain the DNA of a person for the purpose of DNA Testing.

The following list provides information about a number of non-standard samples that can be used to obtain DNA for testing purposes.

1. Direct Biological Samples

Hair

Any hair submitted must have roots or the follicle attached. Hair that is cut will not produce significant DNA. When submitting a hair sample, one must make sure not to touch the part with the follicle as much as possible to avoid contamination. The hair can be sent in a normal plastic or paper envelope and marked clearly as a non-standard sample. The lab will normally require a minimum of 6-10 hairs (or as many as possible) depending on what is available. The more the hairs available, the more the chance of obtaining a DNA profile from them.

Blood

Blood samples can take various forms including whole blood, blood spots on paper or other material (tissues, clothing, and furniture), dried blood etc. Blood used to be the most common form of submitting DNA samples for DNA paternity testing until the advent of buccal swabs. It now rarely requested as it is an invasive procedure as opposed to the non-invasive and painless nature of a buccal swab. Fresh blood sent in a normal tube will provide a more than enough sample for obtaining DNA. In cases where blood is sent as spots on some form of material, then the success of the extraction will depend on the state of the blood and whether it has been exposed to possible contamination such as the elements, human contamination and/or chemical agents.

Nails

It is also possible to extract DNA from Nails. Freshly trimmed nails work best and have the highest chance of success. Nails are normally recommended (apart from hair) in cases where the person has recently died. It is important to handle the nails with minimal direct contact as possible to avoid contamination. The nails can be sent in a normal plastic or paper envelope and marked clearly as a non-standard sample.

Sperm

In the case of liquid semen, it is recommended that the sample is absorbed through a clean cotton swab and air-dried for about one hour. In the case of dried semen stains, either send the material directly to the laboratory or else absorb the stain onto a clean cotton swab moistened with distilled water. Then air-dry for about an hour. The samples can then be sent in sent in a normal plastic or paper envelope and marked clearly as a non-standard sample.

Bone

Bone samples are one of the most difficult materials to obtain DNA from and not all DNA laboratories offer the service. The success rate will depend on the condition of the bones (e.g. how long the person has been dead, how his body has been preserved etc). When submitting bone samples it is normally recommend that fragments from the shaft of the femur or humerus are obtained weighing approximately 2 grams per individual. It is recommended that the laboratory processing the sample is contacted prior to taking the samples to discuss the case in advance. Collection of samples should be performed by a qualified person.

2. Everyday items that may contain DNA for testing purposes

Cigarette Butt

Cigarette butts can be an excellent source of DNA if the sample has not been contaminated. The more the cigarette has been smoked the more DNA is likely to be available. If the cigarette has been shared it is likely that a mixed DNA profile will be obtained, in which case more specialised analysis will be required to separate the profiles. The client should make sure that the sample is not handled from the end used to inhale the smoke. Ideally the client will submit 2-4 cigarette butts if available. The butt can be sent in a normal plastic or paper envelope and marked clearly as a non-standard sample.

Toothbrush

A toothbrush can be a good source of DNA if the sample has not been contaminated. The more the toothbrush has been used the more DNA is likely to be available. If the toothbrush has been shared it is possible that a mixed DNA profile will be obtained in which case more specialised analysis will be required. The client should make sure that the sample is not handled from the end of the bristles to avoid contamination. Also the brush should be air dried for about 30-60 minutes to ensure that it is properly dried before sending to the laboratory. The toothbrush can be sent in a normal plastic or paper envelope and marked clearly as a non-standard sample.

Envelope and Stamp

Licked envelopes and stamps can provide a source of DNA for paternity testing purposes. However, the success rate on this type of sample can very widely since it is not always possible to know if the stamp and envelope have been licked or not. In cases where there has been no contact with a person’s saliva then it is clearly not possible to obtain DNA. Because of this, the sample is normally classified as having a low rate of extraction success rate. When submitting the sample, it is important to ensure not to touch the seals and the back of the stamp to minimise possible contamination.

Chewing Gum

Chewing gum can be a good source of DNA if the sample has not been contaminated by exposure to contaminating agents. Sugar free gum is preferred to normal type of gum. It is important to try not to touch the gum with the fingers as this can lead to contamination. The gum can be sent in a normal plastic or paper envelope and marked clearly as a non-standard sample.