Genetic Anthropology: New Understanding through Genetic Testing Essay

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Genetic Anthropology is the study of combining DNA evidence with physical evidence to understand the history of modern human. These scientists and anthropologists are trying to understand where and when the branches of ancient and modern human existed (U.S. Department of Energy Genome Program, 2010). This field of research focuses on two main ideas. The first focus is to develop a data base of living human to compare genetic markers. These genetic markers will show how different cultures relate to each other. The second focus is to compare current genetic markers to the fossil found in the field to develop an evolutionary track of human migration and try to find out how modern humans evovled (Marks, 2012).

There are many models of how Homo saipan evolved. The Multiregional Continuity Model suggests that Homo erectus left Africa and moved into the Middle East, Europe, and Asia. Then these different groups evolved simultaneously into Homo saipan without direct connection to each other. The other main theory is the Out of Africa Model. This model suggests that Homo saipan evolved in Africa and then migrated into the Middle East, Europe and Asia. The leading theory in Genetic Anthropology is the Out of Africa Model (Johanson, 2001).

DNA studies indicate that all modern humans have a common female ancestor through the use of PCR. By looking at mitochondrial DNA, this common female ancestor, genetic Eve, lived in Africa about 140,000 years ago. The genetic Adam lived in Africa about 60,000 years ago by looking at mutations in the Y chromosome DNA. Other fossil evidence suggest that homo Saipan was not the only homo species living at the time and homo saipan still shares some common DNA markers from these other homo species. These ancestors of homo Saipan are now part of a growing fossil record of ancient human migration patterns indicating that modern humans arose from sub-Saharan Africa about 65,000 years ago. These modern humans moved to southern Asia, China, Java, and later Europe over the next 65,000 years (U.S. Department of Energy Genome Program, 2010).

Scientists use two forms of DNA to understand the different generations. The Y chromosome is passes only from father to son. The Y chromosome allows scientists to trace paternal lineages. Plus, mitochondrial DNA (mtDNA) is passed from mother to child and allows scientists to trace maternal lineages. Both Y chromosome DNA and mtDNA will go through harmless mutations that become genetic markers for certain populations. As different species of humans migrated scientists can look for these genetic mutations in different populations and the age of the fossil will show when these groups lived (U.S. Department of Energy Genome Program, 2010).

Mitochondrial DNA is found and made in the mitochondria of a cell. Mitochondria are structures within the cell that convert energy that the body takes in to energy that the cell can use. Every cell has thousands of mitochondria that surround the nucleus in the cytoplasm of a cell (Genetics Home Reference, 2012). Mitochondrial DNA can only be passed down from mother to children, thus only daughters will pass this genetic information to the next generation of children. This genetic information can be used to develop phylogenetic tree for modern humans evolved (Sorenson Molecular Geneaolgy Foundation, 2007).

Y chromosome DNA is present in males. Since there is only one copy of the Y chromosome from each male, there is no recombination with each new generation. Instead, the Y chromosome is passed down directly and nearly unchanged from a father to a son. Y chromosome DNA only gives information about the direct paternal line. However, since Y chromosome DNA only has subtle mutations, its genetic information can be used to develop phylogenetic information (Sorenson Molecular Genealogy Foundation, 2007).

Researchers use DNA mutation to develop the phylogenetic trees. Most genetic mutations are harmless, but a small fraction can cause disease. Over generations more mutations will occurs, yet people who are closely related will have very few differences in DNA. In 99.9% of modern humans the genome is the same, which is why researchers use the one one thousandth which is different to look at our ancestors migration patterns. This is why researchers use Y chromosome DNA and mtDNA to compare genetic markers and the researchers compare the haplotype to determine common ancestors. Haplotype are groups of people that have the same genetic mutations. Different haplotype groups show where modern humans were as they migrated and researchers will use the fossil record to age these groups (Sorenson Molecular Genealogy Foundation, 2007).

Contemporary studies of DNA have shown that DNA in modern humans is relatively homogenous. Especially in mtDNA, the relatively small mutations make tracking certain significant mutation easier so researchers can create a phylogenetic map of modern humans. Genetic testing of different ethnic groups, both current and fossil record, has shown that African populations have the highest degree of genetic variation in their mtDNA (Johanson, 2001). Moreover, in a study analyzing mtDNA from many different groups of people came up with the conclusion that a single group of Homo sapiens can out of Africa. This study concluded that a group of 10,000 to 50,000 people left Africa around 65,000 years ago due to the limited amount mtDNA mutations (Rogers & Harpending, 1992).

One question that came out of the Out of Africa theory was did modern man share mtDNA with Neandertals. Researchers took samples of DNA from a Neandertal-type specimen found in 1856 in Germany. Neandertals, Homo neanderthalensis, are an extinct group of hominids that were in Europe and western Asia about 300,000 to 30,000 years ago. Modern humans coexisted with Neandertals. With the invention of PCR, DNA from these ancient hominids could be sequences using mtDNA. DNA that is older than 100,000 year is difficult to replicate because fossil remains degraded by hydrolytic and oxidative damage. Since some fossil of Neandertals fall into the desired range, PCR can be used (Krings, et al., 1997). Using overlapping PCR products, mtDNA was taken from the specimen. This sample was compared to mtDNA from 994 modern humans through phylogenetic analyses.

The PCR assay extract from .4 grams of Neandertal bone contained 1000-1500 Neandertal mtDNA molecules of 100bp length. This amount of mtDNA is enough to sequences, yet is much smaller than a typical sample. The researchers extracted DNA and amplified using two primers. The PCR found 27 different segments of mtDNA. Twelve sequences were exclusively Neandertal sequences, six sequences were similar to modern humans and 9 sequences were found to be similar, but had mismatches to the primer. The analysis found that the Neandertal mtDNA sequence falls outside the variation that would link Neandertals to modern human. These findings suggest that Neandertals were a different branch of the Homo species and that modern human were not direct decadences (Krings, et al., 1997). How do researchers use DNA samples to construct phylogenetic trees? Many researchers compare DNA samples looking for certain genetic markers to construct a genotype and phylogenetic-tree.

For example, researchers looked at the Y chromosome biallelic loci during the modern human migration from North Africa to Eastern Asia. The researchers took a sample of DNA from 925 males. The majority of DNA samples were from eastern-Asian populations, while the rest came from previous studies analyzing other groups from Africa, Europe and Native people of the Americas. A total of 19 Y chromosome biallelic loci were looked. A PCR assay was performed to look for these markers. For each genetic Y chromosome mutations, two allele-specific primers were used to recognize the genetic markers. Once PCR was done, the products were arranged into a phylogenetic tree to evaluate the migration patterns of modern humans by where these genetic markers have been seen before. In all the individuals studied, 19 Y chromosome biallelic markers were identified and 17 different Y haplotypes were obtained. Researchers use the Y haplotypes to develop the phylogenetic tree.

The study found H5 Y haplotype had a common ancestor to the subjects that were from Eastern Asia, which supports the theory of an out-of-Africa migration. This theory is supported because H5 and all derivatives have a C→G mutation at the locus M9, yet all African haplotypes have a C at this locus. Researchers hypothesis that the mutations occurred as humans migrated from northern Africa to eastern Asia (Su, et al., 1999). Many different studies have been done and support the Out of Africa theory of evolution.

The map below shows how a theory of how modern humans moved out of Africa using mtDNA and Y chromosome DNA. The National Geographic Societys Genographic Project and other groups have gathered 650,000 genetic markers from mtDNA and Y chromosome DNA to provide clues to how modern humans moved out of Africa. Y chromosome evidence is shown with blue arrows and mtDNA is shown with yellow arrows. As more research and genetic information is gathered, more clues to human evolution will be revealed (Roach, 2008).

Works Cited

Genetics Home Reference. (2012, 12 17). What is mitochondrial DNA? Retrieved 12 18, 2012, from Genetics Home Reference: http://ghr.nlm.nih.gov/handbook/basics/mtdna Johanson, D. (2001, May). Origins of Modern Humans: Multiregional or Out of Africa? Retrieved Decemeber 15, 2012, from American Institute of Biological Sciences: http://www.actionbioscience.org/evolution/johanson.html Krings, M., Stone, A., Schmitz, R. W., Krainitzki, H., Stoneking, M., & Paabo, S. (1997). Neandertal DNA Sequences and the Origin of Modern Humans. Cell, 90(1), 19-30. Marks, J. (2012). The Origins of Anthropological Genetics. Current Anthropology, 53(5), 161-172. Roach, J. (2008, January 21). Massive Genetic Study Supports Out of Africa Theory. National Geographic News, pp. 1-2. Rogers, A. R., & Harpending, H. (1992). Population growth makes waves in the distribution of pairwise genetic differences. Molecular Biology and Evolution, 9, 552-569. Sorenson Molecular Genealogy Foundation. (2007). Mutation and Haplotype. Retrieved 12 17, 2012, from The University of Utah: http://learn.genetics.utah.edu/content/extras/molgen/mutation_haplotype.html Sorenson Molecular Genealogy Foundation. (2007). Y Chromsome DNA. Retrieved 12 17, 2012, from The University of Utah: http://learn.genetics.utah.edu/content/extras/molgen/y_chromo.html Sorenson Molecular Geneaolgy Foundation. (2007). Mitochondrial DNA. Retrieved 12 17, 2012, from The Univeristy of Utah: http://learn.genetics.utah.edu/content/extras/molgen/mito_dna.html Su, B., Xiao, J., Underhill, P., Deka, R., Zhang, W., Akey, J., . . . Du, R. (1999).
Y-Chromsome Evidence for a Northward Migration of Modern Humans into Eastern Asia duing the Last Ice Age. The American Journal of Human Genetics, 65(6), 1718-1724. U.S. Department of Energy Genome Program. (2010, 02 11). Genetic Anthropology, Ancestry, and Ancient Human Migration. Retrieved 12 16, 2012, from Human Genome Project Information: http://www.ornl.gov/sci/techresources/Human_Genome/elsi/humanmigration.shtml

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