The girl with Neanderthal and Denisovan parents
Neanderthals
and Denisovans are distinct groups of hominins that diverged 390,000
years ago. Their DNA has been detected in both ancient and present-day
individuals, indicating past gene flow between archaic and modern
hominins. However, direct evidence for genetic mixing between
overlapping populations is limited, and the closest reported association
is a modern human (Oase 1) with a Neanderthal ancestor within four to
six generations. Now, a study in Nature characterizes the genome of Denisova 11, a first-generation offspring of Neanderthal and Denisovan parents.
O Denisova 11, um fragmento de osso encontrado ao lado de mais de 2.000 outros na Caverna Denisova (Rússia), já havia demonstrado ter mais de 50.000 anos e ter DNA mitocondrial de Neanderthal (mtDNA). Neste novo estudo, a análise genômica indica que Denisova 11 era uma fêmea que, com base na espessura do fragmento ósseo, tinha pelo menos 13 anos de idade no momento de sua morte.
Para saber mais sobre sua ancestralidade, seu genoma foi comparado aos genomas de Neanderthal (Neanderthal Altai) e Denisovan (Denisova 3), ambos obtidos de ossos encontrados na caverna de Denisova. O genoma Denisova 11 continha uma proporção similar de alelos neandertais (38,6%) e Denisovan (42,3%), indicando que ambos os grupos hominíneos contribuíram igualmente para sua ascendência - ou ela pertencia a uma população mista neandertal-Denisovan ou um de seus pais era Neanderthal (sua mãe, com base na análise prévia de mtDNA) e o outro Denisovan.
Credit: EyeEm/Alamy
To
distinguish between these two scenarios, the researchers estimated the
heterozygosity of the Denisova 11 genome by measuring the frequency of
transversion polymorphisms. It was four times more heterozygous than
sequenced genomes from Neanderthals (Altai Neanderthal and Vindija
33.19) and Denisovans (Denisova 3).
Further analysis of transversion sites that were homozygous for different alleles in Altai Neanderthal and Denisova 3 showed that the proportion of heterozygous sites (that is, sites with one Neanderthal allele and one Denisovan allele) in Denisova 11 was consistent with her having inherited one set of chromosomes from a Neanderthal and the other set from a Denisovan. This conclusion was further supported by coalescent simulations that accounted for likely genetic differences between Denisova 11’s ancestors and Altai Neanderthal and Denisova 3, and by the observation that heterozygous sites were evenly distributed throughout the Denisova 11 genome.
Further analysis of transversion sites that were homozygous for different alleles in Altai Neanderthal and Denisova 3 showed that the proportion of heterozygous sites (that is, sites with one Neanderthal allele and one Denisovan allele) in Denisova 11 was consistent with her having inherited one set of chromosomes from a Neanderthal and the other set from a Denisovan. This conclusion was further supported by coalescent simulations that accounted for likely genetic differences between Denisova 11’s ancestors and Altai Neanderthal and Denisova 3, and by the observation that heterozygous sites were evenly distributed throughout the Denisova 11 genome.
Em seguida, os pesquisadores começaram a investigar a ascendência da mãe de Neanderthal de Denisova 11 e do pai de Denisovan. Eles identificaram pelo menos cinco regiões, cada ~ 1 Mb de comprimento, que eram homozigotas para o DNA neandertal, indicando que seu pai tinha algum ancestral neandertal.
The number and size of these regions, along with their high heterozygosity relative to Altai Neanderthal and Vindija 33.19, suggested that he had one or more distant Neanderthal ancestors and that they came from a different population to that of Denisova 11’s mother. Analysis of Denisova 11’s Neanderthal genetic heritage demonstrated that her mother was more closely related to Vindija 33.19 — who lived around 40,000 years later in Western Eurasia — than to Altai Neanderthal, who lived in the same cave 20,000 years before her. This observation suggests that Siberian Neanderthals migrated to Western Europe sometime after the existence of Denisova 11 and/or Western European Neanderthals migrated to Denisova Cave before that time.
The number and size of these regions, along with their high heterozygosity relative to Altai Neanderthal and Vindija 33.19, suggested that he had one or more distant Neanderthal ancestors and that they came from a different population to that of Denisova 11’s mother. Analysis of Denisova 11’s Neanderthal genetic heritage demonstrated that her mother was more closely related to Vindija 33.19 — who lived around 40,000 years later in Western Eurasia — than to Altai Neanderthal, who lived in the same cave 20,000 years before her. This observation suggests that Siberian Neanderthals migrated to Western Europe sometime after the existence of Denisova 11 and/or Western European Neanderthals migrated to Denisova Cave before that time.
“mixing between hominin groups occurred frequently when populations overlapped”
O genoma de Denisova 11 fornece evidências de pelo menos duas instâncias de mistura genética entre grupos hominíneos - uma vez entre seus pais e pelo menos uma vez na ascendência de seu pai. O fluxo de genes foi agora detectado em dois dos seis genomas recuperados da Caverna Denisova (Denisova 3 e Denisova 11) e um dos três genomas recuperados de humanos modernos que coexistiam com hominídeos antigos (Oase 1).
A frequência de tais genomas sugere que a mistura entre grupos hominínicos ocorreu com frequência quando as populações se sobrepunham e que barreiras geográficas e temporais, ao invés de reprodutivas, contribuíram para que os neandertais e os denisovanos permanecessem geneticamente distintos.
A frequência de tais genomas sugere que a mistura entre grupos hominínicos ocorreu com frequência quando as populações se sobrepunham e que barreiras geográficas e temporais, ao invés de reprodutivas, contribuíram para que os neandertais e os denisovanos permanecessem geneticamente distintos.
References
Original article
Slon, V. et al. The genome of the offspring of a Neanderthal mother and a Denisovan father. Nature 561, 113–116 (2018)
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