Archaeogenetics

Archaeogenetics is the study of ancient DNA using various molecular genetic methods and DNA resources. This form of genetic analysis can be applied to human, animal, and plant specimens. Ancient DNA can be extracted from various fossilized specimens including bones, eggshells, and artificially preserved tissues in human and animal specimens. In plants, Ancient DNA can be extracted from seeds, tissue, and in some cases, feces. Archaeogenetics provides us with genetic evidence of ancient population group migrations, domestication events, and plant and animal evolution. The ancient DNA cross referenced with the DNA of relative modern genetic populations allows researchers to run comparison studies that provide a more complete analysis when ancient DNA is compromised. Archaeogenetics is the study of ancient DNA using various molecular genetic methods and DNA resources. This form of genetic analysis can be applied to human, animal, and plant specimens. Ancient DNA can be extracted from various fossilized specimens including bones, eggshells, and artificially preserved tissues in human and animal specimens. In plants, Ancient DNA can be extracted from seeds, tissue, and in some cases, feces. Archaeogenetics provides us with genetic evidence of ancient population group migrations, domestication events, and plant and animal evolution. The ancient DNA cross referenced with the DNA of relative modern genetic populations allows researchers to run comparison studies that provide a more complete analysis when ancient DNA is compromised. Archaeogenetics receives its name from the Greek word arkhaios, meaning 'ancient', and the term genetics, meaning 'the study of heredity'. The term archaeogenetics was conceived by archaeologist Colin Renfrew. Ludwik Hirszfeld was a Polish microbiologist and serologist who was the President of the Blood Group Section of the Second International Congress of Blood Transfusion. He founded blood group inheritance with Erich von Dungern in 1910, and contributed to it greatly throughout his life. He studied ABO blood groups. In one of his studies in 1919, Hirszfeld documented the ABO blood groups and hair color of people at the Macedonian front, leading to his discovery that the hair color and blood type had no correlation. In addition to that he observed that there was a decrease of blood group A from western Europe to India and the opposite for blood group B. He hypothesized that the east-to-west blood group ratio stemmed from two blood groups consisting of mainly A or B mutating from blood group O, and mixing through migration or intermingling. A majority of his work was researching the links of blood types to sex, disease, climate, age, social class, and race. His work led him to discover that peptic ulcer was more dominant in blood group O, and that AB blood type mothers had a high male-to-female birth ratio. Arthur Mourant was a British hematologist and chemist. He received many awards, most notably Fellowship of the Royal Society. His work included organizing the existing data on blood group gene frequencies, and largely contributing to the genetic map of the world through his investigation of blood groups in many populations. Mourant discovered the new blood group antigens of the Lewis, Henshaw, Kell, and Rhesus systems, and analyzed the association of blood groups and various other diseases. He also focused on the biological significance of polymorphisms. His work provided the foundation for archaeogenetics because it facilitated the separation of genetic evidence for biological relationships between people. This genetic evidence was previously used for that purpose. It also provided material that could be used to appraise the theories of population genetics. William Boyd was an American immunochemist and biochemist who became famous for his research on the genetics of race in the 1950s. During the 1940s, Boyd and Karl O. Renkonen independently discovered that lectins react differently to various blood types, after finding that the crude extracts of the lima bean and tufted vetch agglutinated the red blood cells from blood type A but not blood types B or O. This ultimately led to the disclosure of thousands of plants that contained these proteins. In order to examine racial differences and the distribution and migration patterns of various racial groups, Boyd systematically collected and classified blood samples from around the world, leading to his discovery that blood groups are not influenced by the environment, and are inherited. In his book Genetics and the Races of Man (1950), Boyd categorized the world population into 13 distinct races, based on their different blood type profiles and his idea that human races are populations with differing alleles. One of the most abundant information sources regarding inheritable traits linked to race remains the study of blood groups. Fossil retrieval starts with selecting an excavation site. Potential excavation sites are usually identified with the mineralogy of the location and visual detection of bones in the area. However, there are more ways to discover excavation zones using technology such as field portable x-ray fluorescence and Dense Stereo Reconstruction. Tools used include knives, brushes, and pointed trowels which assist in the removal of fossils from the earth. To avoid contaminating the ancient DNA, specimens are handled with gloves and stored in -20 °C immediately after being unearthed. Ensuring that the fossil sample is analyzed in a lab that has not been used for other DNA analysis could prevent contamination as well. Bones are milled to a powder and treated with a solution before the polymerase chain reaction (PCR) process. Samples for DNA amplification may not necessarily be fossil bones. Preserved skin, salt- preserved or air-dried, can also be used in certain situations. DNA preservation is difficult because the bone fossilisation degrades and DNA is chemically modified, usually by bacteria and fungi in the soil. The best time to extract DNA from a fossil is when it is freshly out of the ground as it contains six times the DNA when compared to stored bones. The temperature of extraction site also affects the amount of obtainable DNA, evident by a decrease in success rate for DNA amplification if the fossil is found in warmer regions. A drastic change of a fossil's environment also affects DNA preservation. Since excavation causes an abrupt change in the fossil's environment, it may lead to physiochemical change in the DNA molecule. Moreover, DNA preservation is also affected by other factors such as the treatment of the unearthed fossil like (e.g. washing, brushing and sun drying), pH, irradiation, the chemical composition of bone and soil, and hydrology. There are three perseveration diagenetic phases. The first phase is bacterial putrefaction, which is estimated to cause a 15-fold degradation of DNA. Phase 2 is when bone chemically degrades, mostly by depurination. The third diagenetic phase occurs after the fossil is excavated and stored, in which bone DNA degradation occurs most rapidly. Once a specimen is collected from an archaeological site, DNA can be extracted through a series of processes. One of the more common methods utilizes silica and takes advantage of polymerase chain reactions in order to collect ancient DNA from bone samples.