Uniqueness of Mitochondrial DNA - Essay Example

Mitochondrial Deoxyribonucleic acid, mtDNA, is found within the cell's mitochondria. Contradictory to most of the cell, the function of which is defined by nuclear DNA, mitochondria have their own DNA; and it is assumed to have evolved separately. This DNA is unique because it is inherited maternally, and only maternally, which allows researchers to trace lineage far back in time (Lyle 2004). Mitochondrial Eve is the name given by researchers to a female that is the most recent common matrilineal ancestor of all living humans. Eve is known due to mitochondrial DNA, and the comparison of DNA sequences from mtDNA reveals a phylogeny. Mitochondrial Eve is thought to have resided in Africa 150,000 years ago. This is accomplished in humans by the sequencing one or more of the hypervariable control regions (HVR1 or HVR2) of the mitochondrial DNA (Schwartz & Vissing 2002). Mitochondrial Eve is referred to as an ancestor who has been hypothesized on the grounds of fossil as well as DNA evidence (Vigilant et al. 1991). Phylogenies are constructed on mtDNA comparison shown that the living humans whose mitochondrial lineages branched earliest from the tree are indigenous Africans, while the lineages of indigenous peoples on other continents all branch off from African lines (Vigilant et al. 1991). Researchers can reason that all humans descend from Africa; and then they migrated out of Africa to populate the rest of the world. If the mitochondrial analysis is accurate, then mitochondrial Eve represents the origin of the mitochondrial family tree. Eve must have predated the mass departure and lived in Africa (Vigilant et al. 1991). Mitochondrial Eve was the most recent matrilineal ancestor of humans alive today. On the other hand, as evident lineages died out, the status of common matrilineal ancestor would have been passed to a descendant of the previous matrilineal ancestor. For case in point, the common matrilineal ancestor of the population alive at the time of our Mitochondrial Eve would have lived still further back in time. Researchers had done a case study to determine the diversity of mtDNA in four ethnic groups in Sierra Leone, the Mende and Temne, which together produce 60 percent of the total population, and two minor groups, the Loko and Limba (Jackson et al.). The nucleotide sequence of the hypervariable 1 (HV-1) region of mtDNA was determined from samples of all four groups. There were 275 HV-1 sequences, and a total of 164 haplotypes were observed (Jackson et al.). Jackson reveals that through analysis of molecular inconsistency indicated that the distribution of these haplotypes within the Limba sample was considerably different from the other ethnic groups. He further states that there was no significant difference between the other groups (Jackson et al.). These distinguishing results show genetic differences that can be observed within different ethnic groups in considerably close proximity of each other. Moreover, Jackson, and his group, observed some mtDNA haplotypes that were similar among the Sierra Leone ethnic groups and that have not been published in any other West African studies (Jackson et al.). As a result, there may be evidence for mtDNA lineages that are unique to this region of Western Africa. The methods of sampling were cheek swabs, using the BuccalAmp DNA Extraction kit according to the manufacturer's specifications, which were taking from 166 unrelated individuals from all four ethnic groups: Mende, Temne, Loko, and Limba (Jackson et al.). These samples were obtained in pre-arranged meetings and males were primarily observed. This was because matrilineal and patrilineal studies were conducted (Jackson et al.). Matrilineal and patrilineal ethnic lineages over three generations were recorded for each individual. The mtDNA haplotypes were determined by analyzing the nucleotide sequence of the hypervariable region (HV-I). HV1 sequences were allied and edited from positions 16001-16480 to ensure the identification of unambiguous polymorphisms (Jackson et al.). 480 bases of HV-I nucleotide sequence was determined resulting in the identification of 164 unique haplotypes (Jackson et al.). All four ethnic group samples were mostly observed once; however, considerable haplotype sharing was present within all Sierra Leone ethnic groups (Jackson et al.). Pervious studies merely focused on discerning origins of modern humans and world wide expansion of human populations, and the same studies show that Africa has the most diverse mtDNA in the world (Ingman et al., 2000). A myriad of documents suggest that the people of Sierra Leone are ethnically diverse (Alie, 1990). In a similar study researchers in India obtained mitochondrial DNA from 23 profiles that were drawn from a diverse cultural, linguistic, and geographical background (Roychoudhury et al. 2000). There was general sharing between mtDNA haplotypes among the population, reconstructed on the basis of restricted fraction length polymorphism (Roychoudhury et al. 2000). This may indicate that a small number of females founded the Indian population, possibly on the first expansion wave out of Africa. Ethnic differentiation occurred through demographic development and geographical dispersal. Researchers have studied 644 mtDNA samples collected from 23 ethnic populations (Roychoudhury et. al. 2000): ten populations from the eastern states of West Bengal, Orissa, and Tripura. One population from the central state of Madhya Pradesh, four populations from the northern state of Uttar Pradesh, and eight populations from the southern state of Tamil Nadu (Roychoudhury et al. 2000). A set of individuals from each population were tested via drawn blood from vein puncture (Roychoudhury et al. 2000). All subjects were unrelated. DNA was taken from each subject using standard protocol. The haplotypes were observed and only one haplotype accounted for about 50 percent of all mtDNA molecules. Thus, it can be contingent that this is the most ancient haplotype in Indian populations (Roychoudhury et al. 2000). In 20 of the 23 study populations, this modal haplotype is the most frequent. Roychoudhury states, "Contemporary India is a land of enormous human genetic, cultural and linguistic diversity. Using data on blood group, serum protein and red-cell enzyme markers, it has been shown that, with the exception of Africa, India harbors more genetic diversity than other comparable global regions (Roychoudhury et. al 2000)." Mitochondrial DNA plays an important role in Forensic science, too. The years 1962 to 1962 play an important role in Boston, Massachusetts were grisly murders sprung up on the radar. These murders would be linked to the "Boston Strangler." All eleven women were murdered in their residence, were sexually molested, and were strangled with a piece of clothing. There had been no forced entry; and the victims either knew the killer or let him in voluntarily. The ghastly murders came to a halt when Albert DeSalvo confessed to the murders (Lyle 2004). It seemed that with the conviction of the Boston Strangler the worst series of crimes to happen in the United States would come to an end. However, when DeSalvo confessed he frequently got many of the details to the crimes wrong (Lyle 2004). It took an updated Forensic science method to unravel the unknown. In October 2000, Mary Sullivan - Strangler's last victim - was exhumed from her grave, 36 years after her death. Tests determined there was a semen satin on her body. Due to the fact the sample was degraded, tests for the presence of spermatozoa and for prostatic-specific protein (p30) were not possible (Lyle 2004). On the other hand, mitochondrial DNA was reveled in the material sample. Investigators obtained blood from Richard DeSalvo, Albert's brother. Mitochondrial DNA is passed down maternally so the brothers would have matching mtDNA; and matching mtDNA from the semen stain with Albert's brothers mtDNA would prove that Albert did commit the murders. The verdict is He did not do it (Lyle 2004). Albeit Albert DeSalvo confessed to the crime of killing Mary Sullivan, scientifically, he did not do it (Lyle 2004). And it took mitochondrial DNA to prove it! In conclusion, mitochondrial DNA, mtDNA, is so unique that it is only inherited maternally. Mitochondrial DNA mutation is known to be extremely rare, mutating approximately every 6,500 years (Lyle 2004). Thus, this preserves the link between several different ethnic groupings. Additionally, while the four ethnic groups in Sierra Leone and the 23 groups in India were different linguistically, culturally, and geographically, they all could be traced back to point of early Africa origin. This also successfully negotiates that mtDNA is extremely important in the field of Forensic science. This technique adds another tool in the toolbox to identify both perprators and human remains, as well as, solve cases. Reference: Alie JAD. 1990. A new history of Sierra Leone. London: Macmillan. Ingman M, Kaessmann H, Pbo S, Gyllensten U. 2000. Mitochondrial genome variation and the origin of modern humans. Nature 408:708-713. Jackson, B et al. Sierra Leone Mitochondrial DNA. Abstract (online) http://www.bumc.bu.edu/Dept/Content.aspxdepartmentid=350&PageID=8508 Lyle, D.P. 2004. Forensics for Dummies. John Wiley & Sons Inc. pg.241-44 Roychoudhury, S, et. al. 2000. Fundamental Genomic Unity of Ethnic India is revealed by Analysis of Mitochondrial DNA. Abstract (online). http://www.ias.ac.in/currsci/nov102000/1182.pdf Schwartz, M, Vissing, J, 2002.Paternal Inheritance of Mitochondrial DNA, New England Journal of Medicine. 347:576-580 Vigilant, L., Stoneking, M., Harpending, H., Hawkes, K., Wilson, A.C., 1991, "African Populations and the Evolution of the Human Mitochondrial DNA", Science 253; pp 1503-1507 Read More