Repeats, deletions and other rare mutations separate humans and chimps

Found at News Daily. Original paper by H. Huges et al. published in Nature.

According to this research it was not normal mutations (i.e. the change of G into T or similar, known as SNPs) which caused the rapid divergence between great apes and monkeys and, later on, also humans from great apes. Instead these were apparently caused by copy number variations, including sequence repeats, deletions and even reversions. These kind of mutations are often associated to dieseases in humans but may have also been the origin of species divergence.

As expected, they found humans and chimps were very close in terms of overall sequence. The main differences lie in copy number variations -- repeats of the same genetic sequence over and over, deletions of the sequence, or even instances in which a sequence runs backward.

Among humans, these variations have been associated with diseases ranging from AIDS to autism. They may also underlie the differences between species, Eichler said.

The analysis suggested that in the ancestral branch of primates leading to humans and the African great apes, the number of these duplications began to increase at the same time that the more classic genetic mutations were slowing down.

Humans and chimps, in particular, tend to have extra copies of these sequences, they reported.

New paper on Chimpanzee and Bonobo genetics

J. L. Caswell, Analysis of Chimpanzee History Based on Sequence Genome Allignments. PLOS Genetics, 2008.

No strong surprising conclussions but interesting anyhow, specially for the connections and parallels that can be drawn on us humans. Among the points touched in the discussion are:

• · That the split between Western and Central chimpanzees involved a much larger effective population than previously thought (around 100,000)
• · That the chimpanzee-bonobo split should be move backwards in time to at least 1.29 million years ago. And, that if the human-chimp divergence age is actually older (8 million years instead of 7), then this event would be coincident with the formation of the Congo river (1.5-2 Myrs BP), that many people belive is at the origin of bonobo speciation.
• · That both chimpanzees and bonobos have large fractions of their genome that are closer to humans than each other, what is quite interesting and promising for future studies of human origins.

My personal note: genetic age estimates are always difficult, esotheric and slippery terrain but one pillar for them is the chimpanzee-human divergence estimate. If this one is 1 million years older than normally believed, all human genetic age estimates would need to be some 15% older, assuming all other assumptions are correct.