The mitochondrial genome is organized as a small circular molecule of DNA, present in hundreds/thousands of copies per cell and characterized by a much greater evolutionary rate than the average nuclear gene. The mitochondrial DNA (mtDNA) is transmitted as a non-recombining unit only through the mother and its variability is originated only by the sequential accumulation of new mutations. During millennia, this process of molecular divergence has given rise to monophyletic units (haplogroups) that are generally restricted to specific geographic areas or population groups. The study of the geographical distribution, the internal variability and the coalescence age of each haplogroup allow us to make inferences about the demographic history of populations, such as dispersals, range expansions, or migrations. During my PhD studies, I analysed the sequence variation of the mtDNA at the highest level of resolution, that of complete sequence (mitogenome), in order to reconstruct the migration events of both human and animal populations. In particular, I mainly focused my research activity on three projects. The first project aimed to date the events that brought to the initial peopling in Sardinia and to clarify the genetic history of Europe. Sardinians are "outliers" in the European genetic landscape and, according to paleogenomic nuclear data, the closest to early European Neolithic farmers. To learn more about the genetic ancestry of Sardinians, we analyzed 3491 modern and 21 ancient mitogenomes from Sardinia and observed that the age estimates of three Sardinian-specific haplogroups are >7800 years, the archeologically-based upper boundary of the Neolithic in the island. This finding supports archeological evidence of a Mesolithic occupation of the island, but also reveals a dual ancestral origin of the first Sardinians. Indeed, one of the Sardinian-specific haplogroups harbors ancestral roots in Paleolithic Western Europe, but the other two are most likely of Late Paleolithic Near Eastern ancestry, and among those that are often assumed to have spread from Anatolia only with the Neolithic. Thus, their ages are compatible with the scenario of a Late Glacial recolonization of Mediterranean Europe from the Near East prior to the migration wave(s) associated with the onset of farming. The second project aimed to further assess the mitogenome variation of Native Americans origin. Specifically, I focused on Ecuador and Peru, two geographical areas of particular interest because of their location along the Pacific coast, in order to shed light on the peopling of South America. Phylogenetic analyses encompassing both novel and previously reported mitogenomes, allowed the identification of 50 new sub-haplogroups and the finding of a number of sub-clades shared with Native Americans from North and Central America, thus increasing the number of founding mtDNA lineages that entered South America from the North. Our phylogeographic analyses confirmed that the North to South expansion was extremely rapid, and most likely occurred along both the Pacific and Atlantic coasts. The third study was aimed to acquire information about the diffusion process of the Asian tiger mosquito Ae. albopictus by analysing the mitogenome variation of representatives from Asia, America and Europe. Phylogenetic analyses revealed five haplogroups in Asia, but population surveys showed that only three of these were involved in the recent worldwide spread. We also found out that a sub-haplogroup, which is now common in Italy, most likely arose in North America from an ancestral Japanese source. During these three years I also contributed to two additional projects whose goals were to reconstruct the ancient migratory events involving the Arabian Peninsula and Eastern Africa by the study of a rare haplogroup named R0a and to acquire new insights on the initial events that brought to the diffusion of domestic cattle (Bos taurus) outside the Near East.

Employing mitogenomes to reconstruct migration and dispersal events

BRANDINI, STEFANIA
2017-01-17

Abstract

The mitochondrial genome is organized as a small circular molecule of DNA, present in hundreds/thousands of copies per cell and characterized by a much greater evolutionary rate than the average nuclear gene. The mitochondrial DNA (mtDNA) is transmitted as a non-recombining unit only through the mother and its variability is originated only by the sequential accumulation of new mutations. During millennia, this process of molecular divergence has given rise to monophyletic units (haplogroups) that are generally restricted to specific geographic areas or population groups. The study of the geographical distribution, the internal variability and the coalescence age of each haplogroup allow us to make inferences about the demographic history of populations, such as dispersals, range expansions, or migrations. During my PhD studies, I analysed the sequence variation of the mtDNA at the highest level of resolution, that of complete sequence (mitogenome), in order to reconstruct the migration events of both human and animal populations. In particular, I mainly focused my research activity on three projects. The first project aimed to date the events that brought to the initial peopling in Sardinia and to clarify the genetic history of Europe. Sardinians are "outliers" in the European genetic landscape and, according to paleogenomic nuclear data, the closest to early European Neolithic farmers. To learn more about the genetic ancestry of Sardinians, we analyzed 3491 modern and 21 ancient mitogenomes from Sardinia and observed that the age estimates of three Sardinian-specific haplogroups are >7800 years, the archeologically-based upper boundary of the Neolithic in the island. This finding supports archeological evidence of a Mesolithic occupation of the island, but also reveals a dual ancestral origin of the first Sardinians. Indeed, one of the Sardinian-specific haplogroups harbors ancestral roots in Paleolithic Western Europe, but the other two are most likely of Late Paleolithic Near Eastern ancestry, and among those that are often assumed to have spread from Anatolia only with the Neolithic. Thus, their ages are compatible with the scenario of a Late Glacial recolonization of Mediterranean Europe from the Near East prior to the migration wave(s) associated with the onset of farming. The second project aimed to further assess the mitogenome variation of Native Americans origin. Specifically, I focused on Ecuador and Peru, two geographical areas of particular interest because of their location along the Pacific coast, in order to shed light on the peopling of South America. Phylogenetic analyses encompassing both novel and previously reported mitogenomes, allowed the identification of 50 new sub-haplogroups and the finding of a number of sub-clades shared with Native Americans from North and Central America, thus increasing the number of founding mtDNA lineages that entered South America from the North. Our phylogeographic analyses confirmed that the North to South expansion was extremely rapid, and most likely occurred along both the Pacific and Atlantic coasts. The third study was aimed to acquire information about the diffusion process of the Asian tiger mosquito Ae. albopictus by analysing the mitogenome variation of representatives from Asia, America and Europe. Phylogenetic analyses revealed five haplogroups in Asia, but population surveys showed that only three of these were involved in the recent worldwide spread. We also found out that a sub-haplogroup, which is now common in Italy, most likely arose in North America from an ancestral Japanese source. During these three years I also contributed to two additional projects whose goals were to reconstruct the ancient migratory events involving the Arabian Peninsula and Eastern Africa by the study of a rare haplogroup named R0a and to acquire new insights on the initial events that brought to the diffusion of domestic cattle (Bos taurus) outside the Near East.
17-gen-2017
mitochondrial; DNA
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11571/1203286
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