RECOMBINANT DNA TECHNIQUES: CLONING AND MANIPULATION OF DNA - A Guide to Methods in the Biomedical Sciences - page 68

that generate much of the energy required by the cell, are transmitted
in a manner distinct from nuclear DNA. Mitochondrial DNA is always
maternally transmitted; consequently, DNA from missing person investi-
gations can be compared with a maternal relative for identification. The
analysis of genetic markers on the Y chromosome aids in the identi-
fication of males since the Y chromosome is transmitted from father
to son.
It should be noted that these methods are not just useful for crime
scene investigative purposes, but can be used to trace ancestry as well.
For example, Y chromosome analysis was used to compare the DNA of
descendents of Thomas Jefferson (yes, our third president) and those
of his slave Sally Hemings. This analysis provided the first conclusive
evidence in support of the theory that the two had at least one child
together while President Jefferson was in his second term of office (28).