Five ul of semen contains approximately the same amount of DNA as 50 ul of blood. Special extraction methods are required to release DNA from sperm heads. Consequently sexual assualt samples can be differentially extracted. Saliva contains cellular material. DNA can be extracted from bite marks, cigarette butts, postage stamps on envelopes, and envelope flaps for DNA analysis.
Bone is one of the best sources of DNA from decomposed human remains.
Even after the flesh is decomposed, DNA can often be obtained from demineralized bone. DNA from bone has been used to identify the repatrioted bones from Vietnam era servicemen, and the remains of the White Russian Romanov family who were executed during the Bolsheviek revolution. Like bones, teeth can also be an excellent source of DNA, long after the rest of the body has decomposed. Most healthy indiividuals, however, do not excrete epithelial cells in their urine. All rights reserved.