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January 30th, 2018 / The Economist, UK

It has over five times as much DNA as the human genome!

THE domestication of wheat and other staple crops in the Levant some 10,000 years ago allowed for persistent settlement above a level of mere subsistence—one possible definition of the beginning of civilisation. Early farmers grew naturally occurring hybrids of wheat, and over time tamed them into a robust, easy-to-harvest and high-yielding species, the history of which is revealed in the genome of modern bread wheat. It is an enormously dense, complicated genome. And unlike the genetic codes of staples like rice, soya and maize, scientists struggled until 2017 to crack it. Why was it so hard to decipher and was it worth the effort?

The genomes of ancient wheats, such as wild emmer, contain more of the DNA base pairs required to create proteins than that of humans. Domesticated hybrids, like bread wheat, are even larger. Bread wheat has nearly six times the number of DNA base pairs as humans (about 17bn compared with humans’ 3bn). That is in part because humans are diploid, with two sets of chromosomes, whereas the chromosomes of bread wheat come in sets of six (which correspond to the three ancient wheats of which bread wheat is a hybrid). Furthermore, the DNA of ancient wheat contained a huge amount of duplication. This means that bread wheat not only contains an enormous amount of genetic information, but that much of it is repeated. That makes decoding its genome complex. With fewer unique pieces, it is harder to fit the jigsaw together. Read more