Tuesday, 15 May 2012

Sequencing of the Gorilla Genome: Another Piece of the Puzzle

Aishwarya Jangam, s4257950

Fig 1  - Genetic variance between
great apes and humans
Ever since the theory of primate evolution was pioneered by Charles Darwin and Thomas Huxley in the late 1800s, extensive research has been done around the genomes of human and great ape genomes (Kilcullen 1996). Recently, Kamilah the gorilla, a western lowland gorilla (Gorilla gorilla gorilla) has become the last of the living great apes to have its genome fully sequenced. (Scally et al. 2012) (Scally et al. 2012). Since gorillas are the second closest relatives to humans following chimpanzees, their genome is of great interest and the results of this study confirmed key similarities between humans and gorillas and reveal several phenomena of great importance to the scientific community (Scally et al. 2012).
The research was carried out through a five-way, whole-genome alignment which compared gorilla human, chimpanzee and orang-utan genomes. (Scally et al. 2012) This format of the study not only allowed comparisons between great apes and humans, but among the great apes themselves .The findings of the study corroborated with the conclusions of previous studies (Hobolth 2011) that chimpanzees (C) are the closest relatives to humans (H) with just a 1.37% genetic variance and that gorillas (G) and orang-utans (O) follow with 1.75% and 3.40% genome variances respectively (Scally et al. 2012).Furthermore, it was noticed that while in 70% of the genomes, C and H genomes were closer to one other than they were to the G genome, out of remaining 30% of the genome, 15% showed a closer resemblance between H and G genomes while the other 15% displayed a greater similarity between C and G.

But does this phenomenon mean that the theory of evolution is defunct? No, in fact if anything it supports primate evolution because it displays something known as incomplete lineage sorting (ILS) (Scally et al. 2012). ILS occurs due to the presence of different versions of the same gene called alleles. Alleles form due to mutational differences and as cells continue to divide, the differences continue to be acquired; this phenomenon is one of the causes of genetic diversity in living organisms (Venema 2011). So when a population divides into species, it is very unlikely that all alleles will continue to exist in all species, instead the presence of alleles is left up to chance. (Venama 2011) Making it expected that H and G might share an allele or possess alleles that are not present in C and vice versa – resulting in the 15% genome similarities noticed.

Another major finding of the study was the identification of the accelerated evolution of similar genes in H and G that was not present in C (Scally et al. 2012). While H and C had been found to share numerous accelerated genes in previous studies; the accelerated evolution of brain-associated genes and genes linked to hearing had been noticed in H but not C, leading scientists to believe that this difference had led to the evolution of language and auditory genes in humans. However, the discovery of the acceleration of the same genes in G in the study has cast serious doubt over the theory (Scally et al. 2012).
The sequencing of the gorilla genome has led to greater understanding of primate evolution by refining conclusions from previous studies as well as bringing new phenomenon to light.

Reference List
Hobolth, A 2011, Incomplete lineage storing patterns among human, chimpanzee, and orang-utan suggest recent orang-utan speciation and widespread selection, Genome Research, vol. 21, pp. 349-356.

Kilcullen, J 1996, Darwin and Huxley, viewed 20 March 2012, http://www.humanities.mq.edu.au/Ockham/y6405.html.

Scally, A et al. 2012, ‘Insight into hominid evolution from the gorilla genome sequence’, Nature, vol.483, pp. 169-175

Venema, D 2011, Understanding Evolution: Speciation and Incomplete Lineage Storing, viewed 20 March 2012, <http://biologos.org/blog/understanding-evolution-speciation-and-incomplete-lineage-sorting>.

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