Mitochondrial DNA and Human Evolution

The origin of humans has always been a subject of great interest. Perhaps you might be the descendant of a family line, one surviving in Africa and the other maintaining the lineage in deep pockets of Europe. Perhaps, the mitochondrial DNA may establish a clear link between a certain descendant and the parent group. Scientists analyze morphological and anatomical evidences that support the theory of evolution of life. Human DNA from diverse cultures is being compared to trace the origins of a particular lineage. There is every possibility that people living in Asia may share their ancestral origins with Americans. The reasons for choosing mitochondrial DNA as the means to study human evolutionary principles are listed below.

• It avoids recombination, although, research suggests that it can combine with the nuclear DNA. The mixing of already mixed sections from the mother and the father creates a garbled genetic history.
• There are several thousand copies of mitochondrial DNA as compared to only two versions of the nuclear one.
• Mitochondrial DNA is inherited maternally. Therefore, the tracking of the genetic line becomes easy. The traits are passed on from a great grandmother to the grandmother to her daughter and so on.
• Its rate of mutation is much faster than nuclear DNA.
• Mitochondrial DNA remains fossilized due to the sheer large numbers.

There are two conditions that determine what amount or type of mitochondria enters the egg during fertilization. In almost all the cases, homoplasmic or single type of mitochondrial DNA enters the egg indicating a slow process of female gamete development. Once the fertilization process gets over, the coding region of mitochondrial DNA mutates at the rate of about 0.017x10^-6/site/year. The hypervariable region is the one with no coding where the rate of mutation is 0.47x10^-6. The rate of mutation of the whole genome is taken into consideration to determine the ancestry, while the descendants analysis reveals the changes in the mitochondrial genome. This method of determining the evolution through mutation of mitochondrial DNA is called the 'phylogenetic method.'

Evolutionary Relationship Determination

There are two methods to determine the phylogenetic relationship between individuals based on DNA research.

Lineage method

Haplogroups are the mutations of a single family of mitochondrial DNA. For instance, a cluster of haplotypes H,I,J signify people of European descent. These groups form a part of a population and are characteristic of that population wherever it migrates. These tests have established the fact that the recent ancestors of humans were native to Africa, some 100,000-200,000 years ago. It can also be inferred from this test, that none of the features of mitochondrial DNA of the Neanderthal man are found in the present day human. But it is just one gene of the human chromosome that gives us these conclusions.

Population method

The process of natural selection and genetic drift compels one to consider the male Y chromosome as a part of the detection, using the phylogenetic process. The local conditions and habitat tend to influence the mutation in humans. For example, people in the tropical regions have a more restive ATP synthesis mechanism than people in the polar regions. This may also produce a difference in the various groups of mitochondrial DNA. Thus, the evolution and migration of human beings can be traced by verifying the rate of conversion of the DNA genome sequences. For example, this theory attributes the origin of present day humans to Africa. The period over which these mutations occurred in the studied species, dates back to the original sequence to a time that indicates early African civilization. If the multi-regional aspect is taken into consideration, humans are said to have evolved from Homo Erectus.

Mitochondrial DNA testing is a bridge between the past and the present of human life. It has lead us into discovering the unknown realms of our roots.