Category: DNA

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Potato foundation story

You may remember a post a few weeks back on the origins of potato late blight. Now comes news of a DNA study which looked at the origin of the European potato itself.

The spud was introduced into Europe via the Canary Islands in the mid-16th century. The authors of the study compared landraces currently grown in the Canaries, which are thought to be the descendents of those early introductions, with material from Chile and the Andes. There has long been controversy about whether European varieties trace their origins to one or the other of these places.

It turns out the answer is probably both: there were

“multiple early introductions of both Andean and Chilean germplasm to the Canary Islands and to Europe,” said Dr. David Spooner, co-author of the Crop Science study.

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European aurochs DNA in domestic cattle

A study  ((Edwards CJ et al., 2007. Mitochondrial DNA analysis shows a Near Eastern Neolithic origin for domestic cattle and no indication of domestication of European aurochs. Proceedings Royal Society B 274:1377-1385)) just published by the Royal Society sheds some light on the genetic relationship between the European auroch and modern European cattle breeds. Cattle were initially domesticated perhaps around 10,000 years ago in Mesopotamia, and independently in India and probably Africa. As animal agriculture spread into Europe from the Middle East, domesticated cattle must have coexisted with wild European aurochs for some time, since aurochs in Europe didn’t die out until much later (in fact, the last aurochs appear to have lived in Poland around 1627). Analysis of contemporary as well as ancient mitochondrial DNA from Middle Eastern and Central European archaeological sites now seems to suggest that European cattle originated solely from Middle Eastern aurochs, and that no introgression of European auroch genes into domesticated cattle occurred during their long coexistence.

However, an earlier study  ((Götherström A et al., 2005. Cattle domestication in the Near East was followed by hybridization with aurochs bulls in Europe. Proceedings Royal Society B 272:2345-2350)) did show that there had indeed been introgression of auroch Y chromosomes into Northern and Central European domestic cattle and that these Y chromosome markers still exist in some European breeds. Of course, what might seem contradictory really isn’t: mitochondria are strictly inherited from one’s mother, and the mating of domestic cows with auroch bulls wouldn’t have left any mitochondrial evidence. It would be interesting to know whether such hybridization occurred surreptitiously or intentionally, which of course would suggest that early framers knew something about the benefits of cross-breeding.

From H. Michael Kubisch.

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Undoing millennia of barley selection

Generations of beer-loving farmers have bred seed dormancy almost entirely out of barley, so that the grains will readily germinate in the malthouse. Unfortunately, that means that malting varieties are sometimes prone to jumping the gun and sprouting before harvest, while the crop is still standing in the field. That means that the grain cannot be used to make beer. Not a good thing.

Fortunately, a PhD student in Australia, a land well known for its love of the amber nectar, has compared the barley genome with that of Arabidopsis and identified some bits which may contain previously unknown dormancy genes. Should a negative effect on pre-harvest sprouting be confirmed in the field – and trials are under way – breeders could use markers for these genes to help them select genotypes which will only sprout where it would do the most good: in the maltings.

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Durum wheat erosion

If there’s a dominant meta-narrative in agricultural biodiversity circles it is that modern breeding programmes relentlessly decrease the genetic diversity of crops, increasing yields and quality but also, as new varieties displace landraces and older varieties in farmers’ fields, depleting the very resource on which they are dependent for continued success. But actually there’s not really that much in the way of hard figures on this process. So a recent paper on what breeding has done to diversity in Italian durum wheat is very much to be welcomed.

The researchers used molecular and biochemical markers to compare genetic diversity among five different groups of durum varieties, ranging from landraces from before 1915, to pure lines derived from landraces in the 30s, to genotypes selected from crosses between local material and CIMMYT lines in the 70s. In general, there was indeed a narrowing of the genetic diversity within these groups over time. In fact, the degree of narrowing was probably underestimated, because only a relatively few of the pre-1915 landraces were still available for analysis. Conserving what is left is all the more important.

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Lactose tolerance: independent origins and strong selective pressure

Michael Kubisch has submitted another post, based on an article in Nature Genetics. Unfortunately the full article and a News and Views piece about it are behind a paywall. However, I’ve done some sleuthing to find a few links that give more details on the story, which I’ve added at the end. As Michael noted, the article is “not about genetic diversity of agricultural species, but how agriculture has affected human genetic diversity”. That’s good enough for us.

The ability to digest lactose, one of the primary carbohydrates in milk, varies widely among adult human populations. In some European countries nearly 90% of individuals can tolerate lactose, while the incidence in some Asian countries is as low as 1%. The inability to digest lactose is caused by a decline in lactase, the enzyme that breaks down lactose into sugars that can be absorbed into the blood stream. This decline starts shortly after weaning and most likely reflects the fact that until animals were domesticated, milk was simply not a staple of human diets. Lactose tolerance, or lactase persistence as it is sometimes called, in turn is facilitated by a continuous production of lactase throughout adulthood. Not surprisingly, lactase persistence appears to be closely linked to whether a population has traditionally practiced a pastoral or an agricultural lifestyle.

This new study examined the incidence of lactase persistence in several African populations. Based on analysis of genetic markers the authors of the study conclude that the trait appears to have evolved not only independently from Europe, but also more than once in Africa itself. Given that the prevalence of the trait is so high in some populations and domestication of milk-producing animals only goes back 12000 years or so, which is a mere blink of an eye in evolutionary times, milk consumption must have provided a significant benefit for human survival.

Those links:

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