The Gorilla Genome Sequence
By Benjamin Newman (41404375)
An international team of scientists, led by Richard Durbin (Sanger Institute, Cambridge, UK) sequenced the genome of the western lowland gorilla (Gorilla gorilla gorilla) using a female individual called Kamilah. The results of this sequencing “Insights into hominid evolution from the gorilla genome sequence”, published in Nature, have led to a re-evaluation of the way humans, chimpanzees and gorillas evolved.
The genome of the western lowland gorilla contains over 3 billion pairs of DNA letters and 21 000 genes. Humans share 98% of the gorilla genome which compares with 99% shared with chimps and 97% for orang-utans (Ghosh, P,2012). This confirms the splits between the four species though the exact timing of those splits (12-16mya for orang-utans, 8.5-12mya for gorillas and 5.5-7mya for chimpanzees) remained uncertain according to the research team (Scally, A., et al, 2012).
Split times and mutation rates for the great apes
However the most interesting result derived from sequencing the gorilla genome is that about 30% of that genome is closer to humans or chimpanzees than the human and chimpanzee genomes are to each other (Scally, A., et al, 2012). This raises the prospect that there may have been interbreeding between all three of the lineages after they split. The researchers believe that this is due to a pattern of fragmentation and extinction that has occurred in ape populations since the middle Miocene (Scally, A., et al, 2012). They go on to suggest that this fragmentation of populations may have caused the great apes’ ancestors to exchange genetic material as a means of survival when their population numbers became too low (Scally, A., et al, 2012).
This theory is given credence by the fact that the eastern lowland gorilla (Gorilla beringei graueri) and the western lowland gorilla split from each other 1.75 mya and now live 1000km apart (Reardon,S, 2012). Comparison of the two genomes shows a pattern of shared heterozygosity, suggesting that the split was not clean and that interbreeding has taken place since the two subspecies split (Scally, A., et al, 2012).
Setting aside the interbreeding of different ancestors, the gorilla genome also provides an opportunity to look at the genes that changed after the gorilla split from humans and chimpanzees. Around 500 genes changed more rapidly than the rest especially those connected to hearing (Scally, A., et al, 2012). Humans have these same genes and after humans split from chimpanzees, these genes also evolved rapidly (Ghosh, P,2012). Those genes were thought to be the reason that humans evolved language and chimpanzees did not but this theory can now be discounted (BBC). Other arresting genetic results include a gene (Arg432Cys) that causes dementia in humans but appears to leave gorillas unaffected.
Researchers hope that the sequencing of the gorilla gene may be used with existing great ape genome sequencing to define the point at which the human race evolved genes that allowed for abstract thought (Ghosh, P,2012). Although not all the developments that led to this point would be genetic, it is believed a gene must exist that helped facilitate the process and as Dr Durbin told the BBC: “This is the question we are all fascinated by” (Ghosh, P, 2012)
Reardon,S, 2012, “Gorilla DNA unlock secrets of our species” New Scientist, http://www.newscientist.com/article/mg21328553.700-gorilla-dna-unlocks-secrets-of-our-species.html
Scally, A., et al, 2012, “Insights into hominid evolution from the gorilla genome sequence”, Nature, 483, 169-175Volume:, http://www.nature.com/nature/journal/v483/n7388/full/nature10842.html#/genetic-diversity-within-gorillaAccessed 12/03/2012
Ghosh, P,2012, “Gorilla genome could hold key to human condition”, BBC News, http://www.bbc.co.uk/news/science-environment-17239059