Shark Research - Whale Shark Genome Just As Big As The Human Genome!

Researchers at Emory University and the Georgia Aquarium have now completed their sequencing of the whale shark (Rhincodon typus) genome. This is the first time a nuclear genome of an elasmobranch has ever been sequenced.

The estimated genome size of the whale shark was 3.44 gigabases (Gb) which puts it on par with our own genome (Homo sapien) at 3.3Gb (1). One barrier to sequencing the genomes of cartilaginous fish is that their estimated genomes tend to be rather large; the genome of only one other cartilaginous fish, the elephant shark (Callorhinchus milii), has been sequenced and this was an attractive candidate for genome sequencing as its predicted genome was less than 1Gb (2). Genetic data for a bony fish, the rainbow trout (Oncorhynchus mykiss), is also available and at 1.9Gb this genome is smaller than that of the whale shark (3).

Using predictive software, the researchers estimated that the whale shark genome has 23,594 protein coding genes, which is very similar to the human genome which has 20,000-25,000 protein coding genes. As might be expected,the smaller genome of the elephant shark has only 18,872 protein coding genes.

Genomic studies like this are important as they not only help us understand more about how the underlying genetic code works to make an entire organism function, but they can also be used to deduce the evolutionary relationships between organisms with a greater degree of accuracy than morphological data. Genetic analysis of whale sharks has already proven that there is not just one global population of whale sharks - as was previously thought - but at least 2, genetically distinct populations.

Whilst this genome is just at the draft stage, the researchers hope to secure funding to continue their work and delve deeper into the genetic data of the whale shark in order to help us learn more about this ocean giant - so watch this space!

The draft genome is available at http://whaleshark.georgiaaquarium.org/.