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Monday, February 3, 2014

Who has the largest genome?

When you think of the largest genomes in the animal kingdom, what comes to mind? Humans? Not even close. Some other type of mammal? Nope. At least it must be a vertebrate, right? Sorry. The largest genome found to date belongs to Locusta migratoria, aka the locust.

A team of dozens of scientists from the Chinese Academy of Sciences and other institutions have managed to sequence the locust’s genome, which weighs in at a whopping 6.5 gigabytes. To put that in perspective, the human genome, with which we’ve managed to be fairly successful, contains a little less than half as much DNA. Why on Earth does a lowly insect need that much DNA?

Many of the genes discovered by the authors may be required for the insects’ Jekyll to Hyde transformation from relatively benign grasshoppers into swarming locusts. As grasshoppers, the insects live solitary lives close to home. However, when their numbers reach a certain threshold where they start bumping into one another, they transmogrify into ravenous swarms that travel up to 100 miles per day. Locusts need whole classes of genes to cope with the energy requirements for long distance flight and to allow them to digest everything they encounter.

However, the main reason that the locust genome is so enormous is that it contains a massive number of repetitive elements. These are fragments of DNA that, due to a replication error, have become duplicated over and over again. This kind of thing can happen in any genome, but locusts seems to be particularly lazy about trimming away the excess DNA.

Wang X, Fang X, Yang P, Jiang X, Jiang F, Zhao D, Li B, Cui F, Wei J, Ma C, Wang Y, He J, Luo Y, Wang Z, Guo X, Guo W, Wang X, Zhang Y, Yang M, Hao S, Chen B, Ma Z, Yu D, Xiong Z, Zhu Y, Fan D, Han L, Wang B, Chen Y, Wang J, Yang L, Zhao W, Feng Y, Chen G, Lian J, Li Q, Huang Z, Yao X, Lv N, Zhang G, Li Y, Wang J, Wang J, Zhu B, & Kang L (2014). The locust genome provides insight into swarm formation and long-distance flight. Nature communications, 5 PMID: 24423660.