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Domestication Bottlenecks

Driveway tomato garden. How much diversity do these plants contain?

Driveway tomato garden. How much diversity do these plants contain?

Crops like tomatoes, even heirloom tomatoes, aren’t found in the wild. Domestication of crops usually involves only a relative handful of individual plants. Narrowing the species down to a few hundred (or possibly even a few dozen plants) means only a limited number of copies of each gene will be carried through and many of the variant copies of the genes present in the wild population won’t be included in that number. Keeping the population small for multiple generation reduces variability even more as by chance some rare version of genes in one generation won’t be passed to any of the offspring in the next.

Genetic bottlenecks happen in the animal world as well. Skin grafts between unrelated Cheetahs aren’t rejected because the animals are so genetically similar their immune system can’t distinguish the grafted skin as being different from its own skin. Even less fortunate are the tasmanian devils who have so little genetic diversity that they are being decimated by a transmissible cancer. After fighting with an infected devil, which has tumors on its face and neck, tiny bits of the cancer will get into an uninfected devil’s wounds, and since the immune system can’t distinguish the foreign cancer cells from the devil’s own cells, the cancer cells reproduce unchecked, the trait that makes normal cancers, produced by mutated versions of our own cells, so deadly. And the solution mentioned in the article, to save the species by protecting 200 individuals, while better than letting them all die, will sacrifice even more genetic variability by subjecting the already inbred devils to a new population (and genetic) bottleneck. (more…)

Potato Breeding

Unfortunately the purple potatoes aren't a Cornell Breed

Unfortunately these purple potatoes aren't one of the Cornell breeds

A lot of people may not share my enthusiasm for the potato genome, hopefully you all enjoy eating potatoes. The stereotype of potatoes is lots of boring sameness one identical to the next.* Reality, as usual, is much more complicated. Tens of thousands of cultivars can still be found in the South American regions where potatoes were first domesticated. In America, breeders are constantly working to bring in desirable traits from those (often really cool looking) breeds and even wild relatives of the potato. They face both genetic barriers (species barriers are bad enough normally, but trying to introgress genes across a tetraploidy can be a mess) and consumer acceptance ones.

This was driven home in a story at the NYtimes about Cornell potato breeders who have developed breeds which grow much better in upstate New York, but run into problems because the potatoes look and taste different than the couple of varieties of potatoes consumers and restaurants are used to (most notably Idaho grown Russet Burbanks**). Cornell Extension has been working on overcoming that barrier providing the potatoes to restaurants and, in what I think is a genius move, culinary schools throughout the region.

If you happen to visit New York farmers markets take a moment to ask sellers about the breeds of potatoes they have for sale.*** The potatoes covered in the story are Salem, Eva (both white potatoes), Lehigh, Keuka Gold (yellow breeds), Adirondack Blue and Adirondack Red (both of which are just the color you’d expect from the name.) Purple potatoes in particular just look really cool, see image above.

*There was a saying about accepting differences that I vaguely remember from a childhood TV show, something along the lines of “People aren’t the same like potatoes, and that’s a good thing because potatoes are boring.”

**The Russett Burbank was developed by a truck gardener outside of New York City called Luther Burbank in the 1800s who was initially inspired to become involved in plant breeding by Charles Darwin’s 1868 The Variation of Animals and Plants Under Domestication. He later moved to California where he became famous plant breeder and, among other things championed the practice of grafting (connecting a cutting from one plant (usually a tree) to the stem of another, which, if done properly grows the two together and the cutting will grow flower and produce fruit like it would normally) a practice at the time condemned as unnatural. <– This info from Mendel in the Kitchen by Nina Fedoroff and Nancy Brown a great resource

***In fact, whenever you’re buying directly from a farmer, if you get a chance, ask about the breed of whatever you’re buying. More often than you’d expect there’s an interesting story about why he or she is growing that particular breed and where it came from.