DNA
sequences
STRs
STRs & individuals
Electrophoresis
DNA length
STR patterns
PCR
Sources
Mitochondrial
DNA
Mitochondrial
patterns
Most cells contain enough DNA to do STR typing, after the amount of DNA has been increased by PCR. Good sources of DNA are blood, even in small stains, other body tissues, and body fluids such as saliva, semen, and urine.
But not all biological specimens can be used for STR analysis, even with PCR amplification. Samples that are old, or stored improperly, can be broken down into pieces too small to analyze. And some biological sources don't have enough DNA to begin with. Hair, for example, can be used for STR analysis only if the root is still attached. The hair shaft alone doesn't have enough of the STR-containing DNA to detect.
Mitochondrial DNA Most of the cell's DNA is in the nucleus. Nuclear DNA genes are present in two copies, one each from your mother and father. But there is another type of DNA in cells which is present in hundreds or even thousands of copies, instead of the two copies of most genes. Mitochondria are small organelles within cells, which make energy for the cell. There are usually several hundred mitochondria, and each has its own small pieces of DNA. Mitochondrial DNA analysis is more difficult than STR analysis, and does not give matches as precisely, but it can be used on poorly preserved samples, and on hair, bones, and teeth.
