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Science - How Tomatoes Lost Their Taste
Turns out these green shoulders are a result of the same gene that controls the amount of sugar present in ripe fruits. When farmers selected for a mutation that produced uniformly red tomatoes, they sacrificed flavor.
[Image description: a hand holding a glass bowl stuffed with red plum and cherry tomatoes. Most of the plum tomatoes have splashes of green on their tops and shoulders.]
With tomatoes it's entirely due selective breeding, since there currently are no genetically modified tomatoes commercially available. The only genetically modified tomato that's ever been sold in the US was the FavrSavr tomato (developed to allow for later picking to increase flavor) but due to low sales it was pulled from the market in 1997.
Although, there may be a new cultivar of GM tomato coming up relatively soon, as the USDA has approved a variety of tomato that's been genetically modified to produce a huge amount of anthocyanins, making the tomato a deep purple throughout the entire fruit. Also interestingly the developer has stated that they plan on selling the seeds to home gardeners.