We work with a fundamental part of the hair, which is the occipital area, because that is where the embryonic phase of the central nervous system begins, that is, it is where more bioinformation accumulates from the hair root. If you do not have hair on the nape, it could even be extracted from the head area. In case of not having it in this area either, it would be extracted from the eyebrows or the nasal area, although it is not the most recommended. Although it would still be a marker that we could use if there was no other alternative. From the neck area down it would not be possible because I would lose a lot of bioinformation.