The Evolution And Gentic Basis Of Human Pigmentation

2702 words - 11 pages

SUMMARY. Studies in the field of ancient DNA began thirty years ago. Key discoveries proved that ancient DNA is an important tool in the search for difficult answers pertaining to our past. Studies on pigmentation genetics showed that adaptation for different UV radiations was the major factor contributing to the formation of the current pigmentation pattern in Europe, but there is evidence which highlights the additional effect of sexual selection. From the various genes described to play a role in the determination of human skin, hair and eye color, HERC2, SLC24A4 and SLC45A2 seem to be most strongly associated with this phenotypic characteristics.

Keywords: ancient DNA, pigmentation genetics, melanin

Introduction
The DNA of archaeological human remains is an important tool in the search for difficult answers on our past: the evolution and the origin of the human species, the origin of our diseases, the genetics and evolution of our phenotypic characteristics. The first results in this field were obtained in 1985 by Pääbo et al from a 2430 years old Egyptian mummy (Kefi, 2011). This study used bacterial cloning to amplify small, old DNA sequences. With the development of improved techniques such as PCR and new generation sequencing technologies, it became possible to isolate and routinely amplify ancient DNA, and to surmount problems related to the alteration of ancient DNA (Rizzi et. al, 2012).
The preservation of ancient DNA depends not only on the age and type of the sample (Grigorenko et. al, 2009), but also on environmental conditions. The alteration of ancient DNA is a consequence of autolysis and microbial degradation, but humidity, high or very variable temperatures and very alkaline or acidic pH also contributes to this effect (Kefi, 2011).
Thus, ancient DNA is difficult to amplify because of the small quantity and size of the DNA fragments, the presence of postmortem chemical DNA modifications and due to the presence of contaminants, in particular modern DNA (Kefi, 2011). The contamination with modern DNA can be prevented by following strict precautionary steps during collection and laboratory work (Hummel, 2003). The main advantage of PCR is the selective amplification of a target region of the DNA. The amplification of otherfragments than the target sequences can thus be avoided. Approaches as Multiplex PCR proved to be a powerful tool for the analysis of small quantities and highly degradated source ancient DNA (Kefi, 2011).
The methods and techniques used depend on the age and type of the sample and the questions the researchers wants answered. The majority of the studies focus on the origin, relationship and migration of human populations, but other studies which focus on the reconstruction of the diet, the determination of sex or of phenotypic characteristics are of interest (Mulligan, 2006). Even though working with ancient DNA is difficult and circumstantial, it represents a more scientific bridge to our past.

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