One of the most interesting questions about hominin development is exactly how many of our missing cousins remain in us. Between 1-4 percent of the modern human genome originates from Neanderthals everywhere except sub-Saharan Africa. In addition, between 4-6 percent of the modern Melanesian genome has been found to be derived from a separate species of archaic hominin, Denisovans. Now, a new article focused on comparing a specific type of genetic variance has found evidence to suggest that Denisovans and Neanderthals made large, long-term positive contributions to the human genome. Our understanding of the effects of these changes is currently limited, but they occur in a rather interesting place .
Most studies comparing differences in human populations (or differences between archaic and modern hominins) focus on adaptive single-nucleotide variants (SNVs). It was a single nucleotide variation that gave archaic Northern Europeans the ability to digest lactose, and the ability to do so is a textbook on human natural selection. The picture below shows the prevalence of adult lactase persistence as a percentage of the total population.
Individual nucleotide variations found in the genome of the Tibetan people are associated with greater acclimatization to high altitude conditions. These originate in the Denisovan genome. While the Denisovan supplement occurred much earlier than the adaptation for adult lactase digestion, both have been preserved (meaning they have persisted since the first development).
This new research is not "focused on SNVs. Instead, it analyzed the modern Melanesian genome for copy number variants (CNV). Copy number variation is when the number of copies of an entire gene varies between individuals. Huntington's disease, for example, is caused when a specific sub-section of the Huntington gene is repeated to the point that it causes altered protein production. CNVs are much larger than SNVs and tend to exert very strong selective pressure. All evidence of is preserved CNVs in the Melanesian population that can be traced to Denisovan or Neanderthalgene would therefore be evidence that these variants provided benefits.
One thing to know in advance is that the impact of CNV on the human genome is an active area of study. The SNVs have historically received much more attention.The discovery of preserved CNVs in the Melanesian population from the archaic Denisovan and Neanderthals are significant in their own right. However, it is still not clear exactly what either variation actually does. Part of the difficulty in analyzing CNVs is that they are much larger than SNVs with a much wider range of potential effects.
Denisovan and Neanderthal Contribution
The researchers found two specific CNVs – one associated with the Denisovan genome, and one associated with the Neanderthals. 79 percent of Melanesians carry a duplication of chromosome 16p11.2 of> 383,000 base pairs (kbp) derived from Denisovans and introduced into the native population 60,000-170,000 years ago.
The second variation was introduced by Neanderthals and is carried by about 44 percent of modern Melanesians. It is located on chromosome 8p21.3 and consists of a ~ 6-kbp deletion and a ~ 38-kbp duplication.
What is particularly interesting about Denisovan's addition to the human genome is its location, according to her travel archive, the specific area 16p11.2 that they identified as Denisovan in its origin is part of a locus that "exhibits an enrichment of complex recurrences. structural rearrangement, which predisposes humans to the second most common genetic cause of autism and accounts for ~ 1% of patients. ”To be more specific, Denisovan CNV is directly adjacent to the region of the chromosome where genes known to be associated with autism are.
This specific part of the human genome is known to be unstable and prone to crime errors. Previous research on 16p11.2 has found that a previous duplicative incorporation of the BOLA2 gene some 282,000 years ago "simultaneously increased the number of copies of a gene associated with iron homeostasis and predisposed our species to recurrent disease-related rearrangements. "
that Denisovan's contribution to the human genome is 1). Enormous 2). Built in the metaphorical swamp 16p11.2 and 3). Highly preserved suggests that it was important to maintain. Neanderthal CNV comprises TNFRSF10D (tumor necrosis factor receptor superfamily 10D). According to the researchers, "TNFRSF10D has been reported as one of the primate-specific genes that is preferentially expressed in ancestral cells in the human fetal neocortex."
What does it all mean?
Honest answer: No one is sure. The researchers theorize that these genes likely conveyed an evolutionary benefit to the Melanesians, probably one linked to their lives in an isolated tropical environment.
"Our results jointly suggest that large CNVs originating in archaic hominins and interested in modern humans have played an important role in local population adaptation and represent an insufficiently studied source of large-scale genetic variation," the authors' studies wrote.
The problems with CNV analysis have made it difficult to apply to date.The application of these techniques suggests that we can see them used more widely in the future, but the new method means that we will find out what these variances are does for a long time to come.
Written by Jessica Hall Feature image is a comparison of Homo sapiens with  to Homo neanderthalensi . Credit: Wikipedia.
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