Scientists discovered a number of the most ancient pieces of DNA hiding in the darkest, most mysterious part of the modern human genome.
These DNA are traced back to Neanderthals and a still unknown human ancestor, according to the findings that will be published in an upcoming issue of the journal eLife. Incredibly, these primitive DNA chunks may still be affecting human life at present.
The Dark Heart Of Chromosomes
Plenty about the human genome remains a mystery, but its "heart" is a particular curiosity. In the center of chromosomes — the part that appears as a pinched-in waist, as a report from University of California, Davis described — are centromeres, which anchors the fibers pulling chromosomes apart during cell division. Centromeres are extremely important in understanding what happens when this process goes wrong and leads to cancer or genetic problems.
However, while centromeres are very important, they also contain plenty of repeating sequences, making the region nearly impossible to map properly. Scientists even call it the dark heart of the chromosome body.
"It's the heart of darkness of the genome, we warn students not to go there," explained senior author Charles Langley, who is a professor of evolution and ecology at UC Davis.
Langley and his colleagues suggested the presence of ancient genes known as haplotypes stretched over sections of the genome, particularly the centromere. Haplotypes are groups of genes that are inherited together during evolution, giving clues about the ancestors of modern humans and the traits inherited from them.
Unlike the other parts of the chromosomes, the centromere stays intact during the formation of sperm or egg cells, which means they're more likely to preserve the ancient haplotypes through generations.
Finding Ancient Parts Of The Genome
To see whether they could identify and map the haplotypes in the centromere, the team first checked if they could find centromeric haplotypes or "cenhaps" in the DNA of fruit flies. Upon finding that they could, the researchers focused on human DNA in the 1000 Genomes Project.
Sure enough, they discovered haplotypes in the centromeres of all the human chromosomes examined. A number of major cenhaps were even traced back to lineages from half a million years ago.
In chromosome 11, the scientists found very different haplotypes of Neanderthal DNA in non-African genomes and these haplotypes appear to have diverged between 700,000 to a million years ago. However, these Neanderthal DNA are still potentially influencing modern humans, particularly the sense of smell. Thirty-four of the 400 genes modern humans have for odorant receptors are found in the chromosome 11 cenhap.
Additionally, chromosome 12 had cenhaps that appear to be even more ancient and archaic than Neanderthal DNA, having been inherited from an unknown human ancestor. While scientists have discovered many ancient hominin species as well as evidence of interbreeding, other species are still a mystery to scientists including this mystery relative that gave modern humans a piece of their genes.