2 of 2

Write now Article Tools

Mitochondrial DNA and human evolution

Mitochondrial DNA is an attractive target to study human evolution for several reasons:
- it is present in numerous copies(several thousand copies exist compared to only two copies of the nuclear genome)
- it does not undergo recombination (although new evidence suggests that it may recombine with the nuclear DNA)
- it is always maternally inherited

- its rate of mutation is significantly faster than that of the nuclear DNA
- given its high copy number, it is often the only DNA that remains in fossilized samples
Heteroplasmy is a condition where an individual has more than one type of mitochondrial DNA, while homoplasmy refers to presence of a single type of mitochondrial DNA. The almost universal homoplasmy in humans points to a bottlenecking early during oogenesis which allows only one type of mitochondrion to enter the egg. Any paternal mitochondria undergo programmed destruction (by ubiquitination) soon after fertilization.
There is a controversy with regards to the rate at which the mitochondrial DNA mutates. The coding region of the mitochondrial genome mutates at a faster rate than nuclear DNA, the rate being about 0.017 X 10-6 /site/year. There is also a non-coding region called the hypervariable region (about 1100 bp long) where the rate of mutation is 0.47 X 10-6 /site/year. When ancestry is estimated taking the mutation rate of the whole mitochondrial genome, it is known as the "phylogenetic method" of tracing evolutionary history while the assessment of the mutation rate of the hypervariable region alone is termed as the pedigree method. The phylogenetic method of determining ancestry is useful to trace out more ancient mutations, while pedigree analysis gives an estimate of recent changes in the mitochondrial genome. This is because of the presence of mutational hot spots which have a far greater rate of mutability than the rest of the mitochondrial DNA.

There are two basic methods by which data obtained from mitochondrial DNA is analyzed to determine phylogenetic relationships:
-lineage based
-population based
Lineage based analysis depends on analysis of haplogroups. Haplogroups are defined by presence of shared mitochondrial DNA mutations and cluster in a particular region (for instance haplogroup L1, 2 and 3 are restricted to Africa while haplogroups H, I and J are characteristic of people of European descent). Haplogroups are a part of a population, i.e. when a population moves; it carries all its haplogroups with

• 1
• 2
• next page >>

Add your voice

Know something about Mitochondrial DNA and human evolution: In search of Eve?
We want to hear your view. Write now!