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The Family of Wheat

The latter is a result of wheat’s amazing family tree. The wheat that produced the bread for that sandwich you had for lunch can trace its ancestry back to two grasses growing in the middle east thousands of years ago and a third growing somewhere along the shores of the mediterranean. The wheat first domesticated in the middle east was already a combination of two native grasses, containing the complete genomes of both. While humans have 23 chromosomes and two copies of each, this wheat had only seven chromosomes and four copies of each (two from each of the grasses that had given rise to it).  This wheat was already a good crop, its seed was spread from tribe to tribe and village to village. And it was somewhere along that journey that wheat encountered the third grass, and one of the offspring generated when pollen from that wild grass landed on wheat growing in some farmers field, instead of being a sterile hybrid as usually happens when dissimilar species mate, was able to reproduce and had a better gluten, the combination of proteins that gives wheat the elasticity to hold together as dough, which lead to better bread and soon bread wheats swept across the continents in many places replacing the older wheats that had been grown before.*****
The problem from a genomicist is that each bread wheat cell how contains 42 chromosomes. Remember each of the grass species that gave rise to wheats had seven chromosomes, each with two copies for 14 chromosomes per cell. Seven chromosomes each from of its parents (for 21) and two copies of each brings us to 42. Which is still four less than human cells, so where’s the problem? The different from the human genome is that each of set of seven chromosomes makes up a closely related yet distinct genome. So as bits of DNA are sequenced it is hard to know whether the pieces their overlap are really from the same part of the genome, or instead related sequences from one of wheats other parents (and located on an entirely separate chromosome). Imagine a giant heap of puzzle pieces from three puzzles each made with identically shaped pieces and make very similar pictures although you don’t know what any of the pictures will look like. That’s what trying to sequence the wheat genome will be like

As promised the second part of my giant entry on wheat. Yesterday I talked about yield and breeding techniques. Today I’m going to talk about where wheat can from, and why, if you ever happen to meet a wheat genomicist, you know you’re in the presence of someone incredibly hard core.

The wheat that produced the bread for that sandwich you had for lunch can trace its ancestry back to two grasses growing in the middle east thousands of years ago and a third growing somewhere along the shores of the mediterranean. The wheat first domesticated in the middle east was already the offspring of two native grasses, containing the complete genomes of both. While humans have 23 chromosomes and two copies of each, this wheat had only seven chromosomes and four copies of each (two from each of the grasses that had given rise to it).  This wheat was already a good crop, its seed was spread from tribe to tribe and village to village. And it was somewhere along that journey that wheat encountered the third grass, and one of the offspring generated when pollen from that wild grass landed on wheat growing in some farmers field, instead of being a sterile hybrid as usually happens when dissimilar species mate, was able to reproduce and had a better gluten, the combination of proteins that gives wheat the elasticity to hold together as dough, which lead to better bread and soon bread wheats swept across the continents in many places replacing the older wheats that had been grown before.*

The problem from a genomicist is that each bread wheat cell how contains 42 chromosomes. Remember each of the grass species that gave rise to wheats had seven chromosomes, each with two copies for 14 chromosomes per cell. Seven chromosomes each from of its parents (for 21) and two copies of each brings us to 42. Which is still four less than human cells, so where’s the problem? The different from the human genome is that each of set of seven chromosomes makes up a closely related yet distinct genome. So as bits of DNA are sequenced it is hard to know whether the pieces their overlap are really from the same part of the genome, or instead related sequences from one of wheats other parents (and located on an entirely separate chromosome). Imagine a giant heap of puzzle pieces from three puzzles each made with identically shaped pieces and make very similar pictures although you don’t know what any of the pictures will look like. That’s what trying to sequence the wheat genome will be like.

*Durum wheat, which is still grown for pasta, is still a tetraploid wheat without the additional chromosomes from the third parent of bread wheats. I guess the gluten of bread wheat doesn’t hold up as well in pasta, the same trait that makes it excellent for breads.

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