Gibbons have such strange, scrambled DNA, it looks like someone has taken a hammer to it. Their genome has been massively reshuffled, and some biologists say that could be how new gibbon species evolved.
Gibbons are apes, and were the first to break away from the line that led to humans. There are , in four genera. They all have small bodies, long arms and no tails. But it鈥檚 what gibbons don鈥檛 share that is most unusual. Each species carries a distinct number of chromosomes in its genome: some species have just 38 pairs, some as many as 52 pairs.
鈥淭his 鈥榞enome plasticity鈥� has always been a mystery,鈥� says of Washington University in St Louis, Missouri. It is almost as if the genome exploded and was then pieced back together in the wrong order.
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To understand why, Warren and his colleagues have now produced the first draft of a gibbon genome. It comes from a female northern white-cheeked gibbon () called Asia.
Cut and paste DNA
Inside the genome, Warren and his colleagues may have identified one of the players responsible for the reshuffling. It is called LAVA, and it is a piece of DNA called a retrotransposon that inserts itself into the genetic code. Seemingly unique to gibbons, LAVA tends to slip into genes that help control the way chromosomes pair up during cell division. By altering how those genes work, LAVA has made the gibbon genome unstable.
鈥淲e believe this is the driving force that causes, for want of a better word, the 鈥榮crambling鈥� of the genome,鈥� says Warren.
However, solving this mystery has created another. Such dramatic genome changes are normally associated with diseases such as cancer, and should be harmful. 鈥淚t鈥檚 a complete mystery still how these genomes are able to pass from one generation to the next and not cause any major issues in terms of survival of the species,鈥� says Warren.
It may be that genomes are much more resilient than anyone expected, says at the University of Chicago. 鈥淭he genome can endure lots of changes and still function.鈥�
Hopeful monsters
Shapiro is one of convinced that such major reshuffling has been crucial throughout evolutionary history. He says it is how new species form. This challenges the standard idea that mutations in one or a few genes are enough to establish a new species.
Shapiro鈥檚 controversial idea has a long history. One of its most famous 鈥� to some, notorious 鈥� proponents was German geneticist Richard Goldschmidt. In 1940, he called the animals produced by genome reshuffling 鈥渉opeful monsters鈥� (). They were 鈥渕onstrous鈥� because they differed hugely from their parents, but they carried the 鈥渉ope鈥� of founding a new species because of those differences.
The first gibbons may well have emerged from a major genome shuffle, says Shapiro, which would make them hopeful monsters.
However, we don鈥檛 know for sure that the shuffling of chromosomes was directly related to the evolution of the various gibbon species, says at Cancer Research UK鈥檚 London Research Institute. Earlier this year, Swanton found evidence that colon cancer in humans becomes particularly malignant when it gains an entire extra set of chromosomes. That means some cancers could also be hopeful monsters.
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