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Wheats and gluten

Sometimes it takes some personal connection to get me motivated enough to try and understand something a little more fully. Laziness, I guess. Anyway, for example, I vaguely knew about the gluten seed storage proteins of wheat and the coeliac disease they cause in about 1% of the population. But I decided to delve a little deeper only when an old friend I hadn’t seen for a while visited today and told me that she was a sufferer, and that she needed to know how to describe the condition in italian so she wouldn’t get into trouble eating in restaurants here in Rome.

Having sorted that out, I was interested to know whether there are differences among wheat species in the “toxicity” of their glutens. You’ll remember that wheat comes in a polyploid series: diploid, tetraploids and hexaploids. And that three distinct genomes are involved: AA, BB and DD. Diploid einkorn (AA) and BB genome species got together to form tetraploid emmer and durum wheat (AABB). And these hybridized with wild diploid Triticum tauschii to make hexaploid (AABBDD) bread wheat.

It turns out that differences in gluten toxicity do exist. An analysis of the ancestral A, B and D genomes of wheat found that DNA sequences associated with 4 peptides that have been identified as triggering a response in coeliac patients are not distributed at random. For example, the B genome sequences analyzed did not reveal any of the “guilty” sequences.

On the basis of such insight, breeding strategies can be designed to generate less toxic varieties of wheat which may be tolerated by at least part of the [coelic disease] patient population.

Oh, and coeliac disease is called celiachia in italian.

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Food composition

The new issue of the Journal of Food Composition and Analysis has reviews of food composition activities in both Latin America and Oceania. I only have access to the abstracts, but I know that in the Pacific a lot of attention is being paid to differences in nutrient composition among varieties of crops like banana, pandanus and giant swamp taro. This is something that might be of interest to the authors of a third paper in the same issue of the journal. They look at differences in micronutrient composition within different cereal species in Mali but fail to mention this varietal dimension. They ascribe the differences to climate and ecology — at least in the abstract. Important, of course, but surely not the whole story. I’m going to try to get hold of the paper.

LATER: So it looks like what they did is collect various different samples of fonio, say, in each of several distinct eco-geographic zones and pool the samples collected in each zone for analysis. Nothing in the paper about trying to collect material with similar varietal names or anything like that. So any differences due to environment will be confounded with genetic variation. Seems to me like an opportunity missed, at best.

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Fido decoded

An article by Elaine Ostrander in the latest American Scientist summarizes recent advances in canine genomics, which have been considerable:

The dog genome has been mapped and sequenced. A host of disease loci have been mapped, and in many cases the underlying mutations identified. Our understanding of how dog breeds relate to one another is beginning to develop, and we have a fundamental understanding of the organization of the canine genome. The issue of complex traits is no longer off-limits. We have begun to understand the genetic portfolio that leads to variation in body size and shape, and even some performance-associated behaviors.

Some snippets:

  1. Between-breed genetic variation is about 27.5% of the total, compared to about 5% between human populations.
  2. Dog breeds fall into 4 main groups: Asian and African dogs, plus grey wolves; mastiffs; herding dogs and sight hounds; and modern huntings dogs.
  3. 75% of the 19,000 genes that have been identified in the dog genome show close similarities with their human counterparts.
  4. Variation in a single gene (IGF1) explains a lot of the size differences among and within breeds.

What to do with all this information?

It is certainly hoped that the disease-gene mapping will lead to the production of genetic tests and more thoughtful breeding programs associated with healthier, more long-lived dogs. It will be easier to select for particular physical traits such as body size or coat color… Finally, canine geneticists will have a chance to develop an understanding of the genes that cause breed-specific behaviors (why do pointers point and herders herd?).