The genome is the sequence of 3 billion molecules that constitute all of a person’s DNA. Nine-tenths of our genes are identical to that of a mouse. It doesn’t tell much. Neither would this: sixty percent of DNA found in the humans is also found in a banana. Where lies the mystery then?
DNA in a molecule is a genetic universe. A difference of .1 in a molecule would make some 3 million genetic differences.
According to recent discovery more light has been thrown into genes by comparing modern humans with the Neanderthal cousins. Present-day humans and their extinct Neanderthal cousins are 99.84 percent identical genetically.
Four years after scientists discovered that the two species’ genomes differ by a fraction of a percent, geneticists said on April 17,2014 they have an explanation: the cellular equivalent of “on”/”off” switches can activate DNA or silence genes. Hundreds of Neanderthals’ genes were turned off while the identical genes in today’s humans are turned on, the international team announced in a paper published online in Science. They also found that hundreds of other genes were turned on in Neanderthals, but are off in people living today.
That may explain anatomical differences between archaic and present-day humans, including Neanderthals’ shorter legs and arms, bowleggedness, large hands and fingers, and curved arm bones. Ancient humans were able to build stronger bodies, better adapted to the physical rigors of Stone Age life. And one might say body enhancing without using steroids or invasive surgeons knife certain genes were switched on. The discovery also underlines the power of those on/off patterns. Together, they add up to what is called the human epigenome, to distinguish it from the human genome.
Chief among the epigenetic differences: a cluster of five genes called HOXD, which influences the shape and size of limbs, including arms and hands. It was largely silenced in both ancient species, the scientists found.One person’s epigenome can vary markedly from another’s due to diet, environment and other factors. It is therefore impossible to know whether the on/off patterns found in Neanderthal genes are typical of the species overall or peculiar to the individual studied.
Other DNA with big differences in on/off patterns between the extinct and present-day humans is associated with neurological and psychiatric disorders including autism, schizophrenia and Alzheimer’s disease. More of the Neanderthal versions were silenced.
In an interview, Liram Carmel of Hebrew Uni., Jerusalem speculated that any given gene might “do many things in the brain.” When dozens of brain-related genes became more active in today’s humans, that somehow produced the harmful side effect of neurological illness.
But the main effect might have been the astonishing leap in brain development that most distinguishes modern Homo sapiens from our extinct cousins.
(ack: reuters/April 17-science)