DNA
sequences
STRs
STRs & individuals
Electrophoresis
DNA length
STR patterns
PCR
Sources
Mitochondrial
DNA
Mitochondrial
patterns
There are no STRs in mitochondrial DNA, so to look at difference between individuals it is necessary to determine the base sequence of the DNA. Mitochondrial DNA is about 16,500 bases in length, but most of this is the same in all people. There are two portions of mitochondrial DNA, called the hypervariable regions, which differ between individuals, so it is only necessary to determine the sequences of these two small regions to characterize a person's mitochondrial DNA. Hypervariable region 1 includes the sequence between bases 16,024 and 16,324. Hypervariable region 2 includes the sequence between bases 63 and 322.
Comparing hypervariable regions It's hard to compare two sequences of 300 bases side by side, so the way mitochondrial DNA is presented is to show only the differences between a particular sample and the very first mitochondrial DNA ever sequenced, called the reference sequence.
For instance, in the hypervariable region 2 pattern shown below, the sequence is exactly the same as the reference sequence except for three bases. Base number 72 is A instead of the reference's T, base number 90 is T instead of the reference's G, and base number 185 is C instead of the reference's G.
72[A] 90[T] 185 [C]
Identification with mitochondrial DNA There are hundreds of different
mitochondrial DNA alleles, so two individuals are likely to have different
alleles. However, there are some common alleles, and of course relatives can
have the same allele, so you can't use mitochondrial DNA analysis to positively
identify an individual in the same way as with STR analysis.
Consider the mitochondrial alleles below:
Linda
84[G] 122[A] 270[G] 296[C]
Mike
73[C]
95[C] 97[A] 115[C] 184[G] 190[T]
Nancy
84[G] 122[A] 270[G] 296[C]
Compare these individuals to the following sample and answer the questions:
73[C] 95[C] 97[A] 115[C] 184[G] 190[T]
