Supervisors: TÜ MRI professor ja Cambridge'i Ülikooli õppejõud Toomas Kivisild ja TÜ MRI professor Richard Villems
Opponent: Professor Peter de Knijff, Inimesegeneetika osakond, Leideni Ülikooli Meditsiinikeskus, Leideni Ülikool, Holland
Analysis of extant DNA variation is widely used in evolutionary studies of anatomically modern humans. Haploid mtDNA and Y-chromosome research show that our ancestors originated in Africa about 200 thousand years ago and colonized other continents after the Out-of-Africa migration. The first part of the given thesis concentrates on the study of modern haploid variation in aboriginal populations of Australia and New Guinea - inhabitants of prehistoric Sahul continent. Despite the fact that traces of anatomically modern humans in Sahul are among the oldest outside of Africa, our knowledge of prehistory of this area is rather scarce. Results of this study is concordant with the evidence for 50 thousand years old occupation of Sahul and show that after the initial colonization genetic contact between Aboriginal Australians and New Guineans was very limited. Moreover, while Aboriginal Australians were heavily isolated from neighboring Asian populations, population of New Guinea experienced mid-Holocene gene flow from southeastern Asia. The second part of the given thesis addresses the genetic basis of skin color difference among modern human populations by analyzing variation within tyrosinase (TYR) gene. Tyrosinase plays central role in the production of skin photoprotective pigments - melanins. The evolutionary model of human skin pigmentation indicates that our skin should be dark enough (i.e. heavily melanized) to protect from high level of damaging UV radiation near the Equator, but light enough to permit for UV-dependent vitamin D biosynthesis at higher geographical latitudes, e.g. Europe and East Asia. Current results show that Europeans bear an excess of non-synonymous substitutions leading to the decreased tyrosinase activity, while sub-Saharan Africans are virtually depleted of this kind of variation. The age of European-specific alleles postdate the split between Western and Eastern Eurasian populations and support the timeframe for European skin depigmentation, which was proposed from the analyses of other pigmentation genes. In addition, populations of East Asia similarly lack non-synonymous TYR alleles, pointing to the parallel evolution of light skin in Eurasia.