Interpretation of sequence data: From data collection through databasing and statistics (Jason Eshleman, Trace Genetics)

When viewed with a microscope, mitochondria are among the most prominent organelles within human cells. They are primarily known for the central role that they play in the generation of metabolic energy. In humans (and most animals), mitochondria are almost exclusively inherited through the mother because eggs (and not sperm) are the major contributor of cytoplasm to zygotes. A typical human cell contains between 1,000 and 10,000 mitochondria to satisfy its energy- production needs. Each of these mitochondria contains a copy of the mitochondrial genome which is very small in comparison to the nuclear genome where STR loci are found (16,569 bp vs. 3.2 billion bp for the genome overall). Within that relatively small genome is a stretch of nucleotides called the “mitochondrial D-loop” that tends to differ in its particular sequence of nucleotides from one maternal lineage to another. Analyses of the mitochondrial D- loop sequences have been very useful to biologists studying the migration patterns of humans another mammals. From a forensic perspective, the presence of 1,000 to 10,000 more copies of mitochondrial DNA than nuclear DNA per cell gives analyses of it a distinct advantage in situations where a sample is not expected to have much DNA associated with it (i.e. a hair shaft or bone) or the DNA within a sample is badly degraded (i.e. after cremation). The utility of mitochondrial DNA sequencing in forensic casework, however has been limited due to:

1) the fact that a single cells fairly frequently contain more than one kind of mitochondria (a situation known as “heteroplasmy”);

2) differences between mitochondrial samples are not easily detected differences in length like those for STRs and must be determined by comparatively costly, technically challenging, and subjective DNA sequencing;

3) like Y-STRs, the rarity of mitochondrial sequences must be determined by empirical studies and the associated statistics are (and will remain) far less impressive than those generated with STR testing;

4) all maternally related individuals are expected to have the same nominal mitochondrial DNA sequence(s); and

5) the ease with which samples are contaminated and cross- contaminated.

Materials

Presentation

Robert Lee Vaughn v. State of Georgia: Application for interlocutory appeal Vol. 1

Robert Lee Vaughn v. State of Georgia: Application for interlocutory appeal Vol. 2

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Last modified: 03/12/10