Nuclear DNA is inherited DNA from both parents, half from each. It is unique for every human being, with the exception of identical twins. Mitochondrial DNA is passed on from mother to child. Although mutations sometimes occur, a person's mtDNA can usually be matched to his or her mother and female maternal relatives. Siblings and sisters' descendants would also have matching mtDNA. Lincoln didn't have a sister or surviving descendants. If the investigators could identify female relatives of Lincoln's mother, it might be possible to find a mtDNA match.
Left: Mitochondrial DNA is passed on from mother to child.
Mitochondrial DNA is not a unique identifier, as it can be passed unchanged to many different individuals in successive generations. MtDNA is useful for eliminating mismatches. When the number of possible DNA contributors is small, matching mtDNA samples are more definitive. (HOLLAND AND PARSONS 31)
Right: DNA sequence match and mismatch.
Nuclear DNA contains coded genetic sequences that determine your hereditary characteristics. Mitochondrial DNA lacks this information, and can only be used to match a sequence of "nonsense" codes. An investigation of Lincoln's mtDNA does not raise the compelling privacy issues associated with nuclear DNA analysis. Genetic analysis of tissue from historical figures has become increasingly commonplace during the past few years, but legal and ethical standards have not yet been established for this type of research. Any proposal to isolate Lincolns' mtDNA must be reviewed and approved by legal and ethical specialists.
Testing for Marfan syndrome is not a part of the Chicago Historical Society's collaborative investigation.
Other investigators have considered DNA testing of purported Lincoln autopsy materials to determine whether the president suffered from Marfan syndrome, the most common inherited connective tissue disorder. This investigation would require nuclear DNA analysis and larger sample sizes. The investigation of the Chicago Historical Society's cloak is limited to mitochondrial DNA identification rather than nuclear DNA analysis.
Loose joints are characteristic of Marfan Syndrome, "The 'Thumb Sign' in Marfan Syndrome," New England Journal of Medicine 333(7): 430, Falk, Rodney H. Copyright 1995 Massachusetts Medical Society. All rights reserved.
