You can still use PAF and a custom field to maintain your DNA data. The DNA information for a specific person should be entered, just like the persons other facts, Date of Birth, Name, etc. What you do with this data is another thing.
An ID is a unique (no duplicates) special piece of data, SSN are ID's in the USA. The total DNA sequence (no two people will have the exact same sequence) is unique and can be used as an ID, however many people can share the same pieces/parts of the DNA strand (as do humans to other animals) these are not unique and are simply *data*.