How They Do DNA Tests

We had a molecular genetics practical the other day in which we used horse hair and extracted the DNA from it. This is the process that many DNA tests are based on so I decided to write a blog on how this was done. I should have taken some photos but I have only just decided. This may not be the method used by all companies doing DNA tests but this is how we did it.

These tests may be carried out for breeding purposes to detect for coat colour genes or genes that may be linked to diseases. See my other post on coat colour and linked diseases.

• During the practical we were given horse hair and we had to cut the follicles off around 20 strands with a scalpel. As it is DNA you are testing for you have to be very careful with contamination.

• Once the hair follicles have been cut off they were put into tiny tubes. Before the DNA can be analysed it has to be removed from the hair follicles. This is done by mixing the hair follicle with certain solutions, the type used may depend on the type of DNA sample. 
• The samples undergo a number of steps such as being heated in a water bath. They are also put into tubes with filters on them. 
• They are spun on a high speed centrifuge machine after adding a number of different solutions.
• The DNA will then be held in the filter, the final solution then removes it from the filter and keeps it in the solution.

• A NanoDrop machine can be used to detect the levels of DNA now present in the solution. This is important when knowing how much to dilute it by before the DNA analysis.

• PCR is then used to look at the DNA present. During this step the DNA solution is mixed with primers which cut the DNA.
• The PCR machine then runs for a number of cycles which last varying lengths of time at certain temperatures.
• PCR separates the two strands of DNA and allows lots of copies of them to be made. This will allow them to be detected when assessing the DNA present.

• The DNA solution is run on gels via electrophoresis using electrical currents to separate the DNA.
• T-RFLP is a machine that can sequence the DNA present. 

• To then tell what this DNA actually means it is compared with known genes using computer programs. The equine genome was sequenced in 2007 so this is now available. It can tell you the types of DNA present along with how much of it is present in the sample.

Here is a little addition to this article. I have just seen a news story on an equine "DNA bank" which would be useful against the theft of horses and recognising who the horse belongs to. They say this is a longer lasting solution than microchips which may be removed. http://www.bbc.co.uk/news/uk-17169712

Love Laura
xxxx