At a slight loss for what to write for today’s factlet this morning, I turned to twitter. Some nice questions on long distance travel and why vertebrates have four limbs came up (I may return to the vertebrate limb question at a later date), but @donalde suggested talking about the genetics of wheat. Seeing as that fits in nicely with my vague bread, cheese, alcohol and comfort food theme for the next couple of weeks, I thought I’d give it a go. I won’t be covering all of the 30,000-odd varieties of wheat, but just some of the most common, and interesting…
One of the first types of wheat to be cultivated by humans (around 10,000 years ago), that is still around today, is called einkorn (a.k.a. Triticum monococcum). In terms of its genetics, einkorn is like you and I – it’s diploid. This means it has two copies of each of its chromosomes in every cell. “So what?” you may say – well, the number of chromosomes gets important later. Domesticated einkorn isn’t found all that commonly any more, but is still used to make a porridge-like dish in parts of France.
The next type of wheat to mention is Triticum turgidum. This arose from a chance mating between a wild form of wheat, Triticum urartu and a type of goatgrass. The offspring of these two was a tetraploid form of wheat – with every cell containing four copies of each chromosome rather than the two copies of its diploid parents. This doubling up of the chromosomes, called polyploidy, was once thought to be more common in plants than in animals, though there is evidence to suggest that it could have played an important role in the evolution of both plants and animals. The tetraploid wheats still feature in our diets today – Durum wheat is used to make the characteristically yellow semolina flour, and to make pasta, and Emmer or Farro is used a bit like barley or rice in Italy.
Yet another chance mating, this time between a Triticum turgidum species and a wild goatgrass around 8,000 years ago, resulted in the hexaploid wheats that we most commonly use (all included in Triticum aestivum), with six copies of each chromosome in their cells. The extra chromosomes are thought to contribute to the versatility of these wheats, particularly their gluten proteins. The hexaploid wheats include T. aestivum aestivum, our common bread wheat, which itself comes in several varieties split up according to the strength of their gluten proteins, and the high-protein grain spelt (T. aestivum spelta). Genetic studies have suggested that European spelt may have arisen from a separate hybridisation of Emmer wheat and bread wheat, making it genetically distinct from Asian spelt, which was the result of T. turgidum hybridising with goatgrass. A note to mention is that although some types of wheat, like spelt, are better tolerated by people with a wheat intolerance, they all still contain gluten that is toxic to people with coeliac disease.
The Science Sponge 