Question: What are degraded sources of DNA? And how will the new methods work in identifying the DNA?

All sources of DNA will degrade given enough time and exposure to the environment. This is because once a cell dies, it breaks open and the DNA can be exposed to the environment. So something like a blood stain can have degraded DNA especially if it is old (even just a few months in some cases). However the most common degraded sources of DNA are usually what lasts in the environment the longest – bones and teeth. Blood and tissue break down pretty quickly in comparison, namely because bones and teeth have lots of mineral in them, and are hard and well protected, and soft tissues don’t have this protection, so are rapidly broken down by microbes and insects and other factors in the environment.

One exception is hair, which is what I work on. It only has tiny amounts of fragmented DNA in the shaft, and this has nothing to do with exposure to the the environment. As the hair grows, the cells break down, and the DNA ends up degraded because of this natural process.

Degraded DNA is damaged and fragmented into very small pieces. Most normal methods we use target larger sequences of DNA, because with fresh DNA used for routine work, the DNA isn’t all fragmented so it works really well. But when you try to analyse fragmented DNA with these methods they just don’t work – the DNA is too broken up to be used for routine methods.

So my new methods are about analysing the small fragments of DNA – this involves targeting single base DNA differences between people rather than long pieces (sequences), as the single bases are going to still be intact in fragmented DNA, whereas a whole piece of DNA won’t be.

Hope that answers your question – the degradation of DNA, and new methods to analyse it is a pretty big (and sometimes complex) area of research!