Perspectives from human Y chromosome – phylogeny, population dynamics and founder events
Kuupäev
2018-11-09
Autorid
Ajakirja pealkiri
Ajakirja ISSN
Köite pealkiri
Kirjastaja
Abstrakt
Rahvastikusündmused on jätnud oma jälje iga inimese genoomi. Täna suudame neid ’lugeda’ nii praegu elavate kui juba ammu surnud inimeste geneetilisest materjalist. Y-kromosoom on eriline genoomi osa, mis pärandub edasi vaid mööda isaliini, kõikide maailma isaliinide omavahlelist sugulust näitab nende ‘sugupuu’. Täna saame ka Y-kromosoomilt ohtralt DNA-lugemeid, mis võimaldavad võrratult täpsemalt hinnata inimese isaliinide mitmekesisust ning harude lahknemisaegu isaliinide puul. Doktoritöös uuriti mineviku rahvastikusündmusi peamiselt inimese Y-kromosoomi andmeid analüüsides.
Töö tulemused näitasid, et inimese kõikide teadaolevate isaliinide viimane ühine eellane elas Aafrikas umbes 250 tuhat aastat tagasi, paljude liinide arvukuse kasv toimus aga viimase 15 tuhande aasta sees. Üllatuslikult leidsime ka, et 4–8 tuhat aastat tagasi kahanes järsult järglasi saavate meeste suhteline arv, samas kui naistel see arv ei muutunud. Kuna sigivate meeste arvukus vähenes samal ajal, kui muutusid inimeste eluviisid – mindi üle küttimiselt ja koriluselt põlluharimisele, võisid need kultuurilised muutused mõjutada meeste reproduktiivkäitumist.
Lisaks näitasime, et Lõuna-Siberist pärit Baikali-äärse 24 000 aasta vanuse ülempaleoliitilise Malta kultuuri esindaja ema- ja isaliin ei ole tüüpilised tänased seal piirkonnas levinud Ida-Euraasia liinid, näidates geneetilise pärandi olulist muutumist läbi aja.
Asutajasündmused, mil uus rahvakild tekib mingi algse grupi väikesest alamhulgast, jätavad uue grupi geneetilisse pärandisse iseloomuliku jälje. Neid analüüsisime Euroopa romi ja aškenaasi leviidi meeste seas. Lõuna-Aasia päritolu H1a1-M82 tüüpi isaliin on levinud ka Euroopa romide seas, viidates nende algkodule. Romide liinidele kõige sarnasemad on Loode- ja Põhja-India meeste seas levinud variandid, viidates võimalikule Romide päritolupiirkonnale. Tüüpiline aškenaasi leviitide isaliin R1a-Y2619 on kõige tõenäolisemalt pärit Lähis-Idast. Näitasime, et see kuulus aškenaasi leviitide asutajaliinide hulka, kuid selle levik oli seotud pigem aškenaasi juutide populatsiooni üldise laienemisega.
Demographic processes have left their traces into every human genome. Today we can ‘read’ them from the genetic material of people living now and those passed away long ago. Mitochondrial DNA and Y chromosome (chrY) are parts of the genome that pass on through maternal and paternal lines. The relationships of all these lineages in the world are captured in a global ‘family tree’ of maternal or paternal lineages. Just recently it became possible to attain high numbers of sequencing reads also from chrY. This enables to assess the variation of human paternal lineages and date their splits on the tree with unmatched precision. This thesis investigates the past demographic events mainly by analysing the sequencing datasets of human chrY. We showed that the most common ancestor of all known paternal lineages lived in Africa about 250 thousand years ago (kya) and many of the now widespread lineages started to expand 15 kya. Then, 4–8 kya the relative number of males who had offspring (Nm) decreased drastically, while in females it did not change. Since the decrease of Nm coincided with the changes of lifestyle from hunting and gathering to farming, the decrease in the number of breeding males could have been caused by cultural forces that influence the reproductive behaviour of men. The maternal and paternal lineages of a southern Siberian 24,000 years-old Upper Palaeolithic individual from near Lake Baikal are not typical East Eurasian lineages found in the area today. This testifies for population changes affecting the genetic make-up of the people living in that region. Founder events during which a new population forms as a small subset of an initial group, leave distinct traces into the genomic legacy of the newly formed group. We analysed these traces in the paternal gene pool of European Roma and Ashkenazi Levites. H1a1a-M82 is a paternal lineage carried by 12% of South Asian men. The same lineage is spread among European Roma whose variants have closest relations to men from north western and northern India, pointing to their potential place of origin. The main lineage among Ashkenazi Levites, R1a-Y2619, originates in the Near East and it was probably carried by the first founders of the Ashkenazi Levites. The increase in numbers of carriers of this lineage was not an event specific to Levites, but part of the general Ashkenazi Jewish expansion.
Demographic processes have left their traces into every human genome. Today we can ‘read’ them from the genetic material of people living now and those passed away long ago. Mitochondrial DNA and Y chromosome (chrY) are parts of the genome that pass on through maternal and paternal lines. The relationships of all these lineages in the world are captured in a global ‘family tree’ of maternal or paternal lineages. Just recently it became possible to attain high numbers of sequencing reads also from chrY. This enables to assess the variation of human paternal lineages and date their splits on the tree with unmatched precision. This thesis investigates the past demographic events mainly by analysing the sequencing datasets of human chrY. We showed that the most common ancestor of all known paternal lineages lived in Africa about 250 thousand years ago (kya) and many of the now widespread lineages started to expand 15 kya. Then, 4–8 kya the relative number of males who had offspring (Nm) decreased drastically, while in females it did not change. Since the decrease of Nm coincided with the changes of lifestyle from hunting and gathering to farming, the decrease in the number of breeding males could have been caused by cultural forces that influence the reproductive behaviour of men. The maternal and paternal lineages of a southern Siberian 24,000 years-old Upper Palaeolithic individual from near Lake Baikal are not typical East Eurasian lineages found in the area today. This testifies for population changes affecting the genetic make-up of the people living in that region. Founder events during which a new population forms as a small subset of an initial group, leave distinct traces into the genomic legacy of the newly formed group. We analysed these traces in the paternal gene pool of European Roma and Ashkenazi Levites. H1a1a-M82 is a paternal lineage carried by 12% of South Asian men. The same lineage is spread among European Roma whose variants have closest relations to men from north western and northern India, pointing to their potential place of origin. The main lineage among Ashkenazi Levites, R1a-Y2619, originates in the Near East and it was probably carried by the first founders of the Ashkenazi Levites. The increase in numbers of carriers of this lineage was not an event specific to Levites, but part of the general Ashkenazi Jewish expansion.
Kirjeldus
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Märksõnad
human genetics, genomes, Y chromosome, population genetics, population dynamics, phylogeny, demographic events