Dogs are not dumbed-down wolves.
Pigs didn’t fly, walked to Europe
We know that agriculture began in the Fertile Crescent about 12,000 years ago and then spread across Europe between 9,000 and 6,000 years ago. But what exactly was it that spread? Was it the idea of agriculture or agriculturalists themselves? Just-published work on the DNA of modern and ancient pigs says it was probably a bit of both. It seems that Middle Eastern farmers migrated into Europe carrying their agrobiodiversity with them — crops and domesticated animals. But, as far as the pig was concerned anyway, they soon adopted a locally domesticated version in preference to the Middle Eastern type they had brought along.
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.
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:
- Between-breed genetic variation is about 27.5% of the total, compared to about 5% between human populations.
- Dog breeds fall into 4 main groups: Asian and African dogs, plus grey wolves; mastiffs; herding dogs and sight hounds; and modern huntings dogs.
- 75% of the 19,000 genes that have been identified in the dog genome show close similarities with their human counterparts.
- 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?).
Backyard domestication
There’s a “dump heap” hypothesis of agricultural origins which suggests that people first got interested in actively managing and manipulating plants for food or other products when they saw them sprouting out of piles of garbage in and about settlements. There they could observe them daily and experiment with them. A slight variation on this theme — involving corrals in pastoralist campsites rather than garbage dumps — has been proposed for the domestication of quinoa.
One of the things that might have happened in these fertile micro-environments in close proximity to human habitations is that different related species might have been brought accidentally together, leading to hybridization and the development of interesting new — polyploid — types. But there really hasn’t been much empirical evidence for this.
No more. A new paper ((Colin E. Hughes, Rajanikanth Govindarajulu, Ashley Robertson, Denis L. Filer, Stephen A. Harris, and C. Donovan Bailey. Serendipitous backyard hybridization and the origin of crops. PNAS published August 17, 2007, 10.1073/pnas.0702193104.)) looks at the domestication of the legume tree Leucaena in Mexico, where it is grown for food (it is also used as a fodder in some parts of the world). A variety of evidence is discussed which suggests that there has indeed been much hybridization among up to 13 different wild species of Leucaena in Mexican backyards. This has proved “a potent trigger for domestication.” The authors think a similar thing also happened in Mexico with two other perennial crops, Agave and Opuntia.