Hair shaft material lacks this mineral matrix, and the keratin structure that makes up most of the hair does not preserve DNA in the same way.

The DNA that does survive in hair is concentrated primarily in the hair root — the bulb at the base of the hair shaft where active cell division was occurring when the hair was last growing.

The shaft itself contains trace quantities of nuclear DNA and somewhat more mitochondrial DNA — the DNA found in the mitochondria, which are cellular organelles rather than the nucleus itself.

Mitochondrial DNA is circular rather than linear, is present in many copies per cell compared to nuclear DNA’s two copies, and survives degradation somewhat better as a result.