Small group scoops international effort to sequence huge wheat genome

Nov 1, 2017

By Ewen Callaway

The wheat genome is finally complete. A giant international consortium of academics and companies has been trying to finish the challenging DNA sequence for more than a decade, but in the end, it was a small US-led team that scooped the prize. Researchers hope that the genome of bread wheat (Triticum aestivum) — described in the journal GigaScience this month[1] — will aid efforts to study and improve a staple crop on which around 2 billion people rely.

The wheat genome is crop geneticists’ Mount Everest. It is huge — more than five times the size of a single copy of the human genome — and harbours six copies of each chromosome, adding up to between 16 billion and 17 billion letters of DNA. And more than 80% of it is made of repetitive sequences. These stretches are especially vexing for scientists trying to assemble the short DNA segments generated by sequencing machines into much longer chromosome sequences.

It’s like putting together a jigsaw puzzle filled with pieces of blue sky, says Steven Salzberg, a genomicist at Johns Hopkins University in Baltimore, Maryland, who led the latest sequencing effort. “The wheat genome is full of blue sky. All these pieces look like a lot of other pieces, but they’re not exactly alike.”

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2 comments on “Small group scoops international effort to sequence huge wheat genome

  • In the human world things that are created by us come with manuals. A basic user manual showing how to operate the device, a more complex workshop manual showing how to strip, check and repair it, even more detail for the manufacturer showing machining operations and material specs. It is a natural function of items created by an intelligent designer that the more complex the item, the lengthier the manual. It seems illogical or even impossible for it to be any other way.

    What strikes me greatly about the natural world is that the size of the workshop / manufacturing manual (the DNA sequence) can bear no relation to the complexity of the organism. We like to think of ourselves as the most complex, or at least most important, creatures on the planet but in fact the genome for flowering plants is often many times the size of the one needed to build a human. Our genome has just over 3 billion base pairs. That of the tiny fruit fly Drosophila Melanogaster which is commonly used in genetics research has only 140 million. Viruses only need a few thousand.

    The Marbled Lungfish which is a fairly primitive African fish has a genome 130 billion base pairs long. However the flowering plant Paris Japonica has a genome even larger at 150 billion base pairs.

    It is utterly inconceivable that an intelligent designer would require a manual 50 times larger to build a flowering plant than the one needed to build a human. The reason of course is that no intelligent designer is involved. Error, duplication and long since redundant sections of code which never got deleted have led to some genomes becoming huge over time while others have stayed proportionate to the complexity of the organisms they code for. Only evolution could account for this. An intelligent designer would never put the redundant bits in there in the first place.

    The single most important difference between evolution and intelligent design is that evolution can’t easily go backwards. It can’t rip up the specs for an earlier model and just write what’s needed for the current model. It has to keep adding to the genome to incorporate each change even when that change means losing a body part that used to be there in the past. We see this with complete clarity in the growth of the human embryo. It doesn’t just grow from a single cell into a human. It has to plough through all the steps that used to be there in the distant past as it works through the pages in the manufacturing manual in sequence. We grow gills and then lose them again because our fish ancestors lived in water. We grow a tail and then lose it again because our primate and reptile ancestors had tails. Every deletion in the final organism compared to the ancient ancestor is still an addition to the ever growing manufacturing manual.

    A human designer would never do this. A god who supposedly created everything on earth from scratch in the space of week certainly wouldn’t. Only billions of years of evolution that kept adding, changing and then subtracting bits again little by little would ever build a body in such a bizarre way.



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  • @OP – The wheat genome is crop geneticists’ Mount Everest. It is huge — more than five times the size of a single copy of the human genome — and harbours six copies of each chromosome, adding up to between 16 billion and 17 billion letters of DNA. And more than 80% of it is made of repetitive sequences.

    Polyploid, hexaploid and tetraploid species multiply up their number of chromosomes and genes beyond that of the normal diploid pairs.

    Wheats are a combination of hybridisation and polyploidy.
    This means they have a collection of related genetically similar, but slightly different ancestors, with some matched genes and a few mutated different ones all bundled together in polyploid genomes.

    https://en.wikipedia.org/wiki/Taxonomy_of_wheat

    In the 1950s growing awareness of the genetic similarity of the wild goatgrasses (Aegilops) led some botanists to amalgamate Aegilops and Triticum as one genus, Triticum. This approach is still followed by some (mainly geneticists), but has not been widely adopted by taxonomists. Aegilops is morphologically highly distinct from Triticum, with rounded rather than keeled glumes.

    Aegilops is important in wheat evolution because of its role in two important hybridisation events. Wild emmer (T. dicoccoides and T. araraticum) resulted from the hybridisation of a wild wheat, T. urartu, and an as yet unidentified goatgrass, probably similar to Ae. speltoides. Hexaploid wheats (e.g. T. aestivum and T. spelta) are the result of a hybridisation between a domesticated tetraploid wheat, probably T. dicoccum or T. durum, and another goatgrass, Ae. tauschii (also known as Ae. squarrosa).



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