It may sound like a matter settled long ago, but why carrots are orange hasn't had a scientific explanation until now. Discovery reports that a team of researchers led by University of Wisconsin–Madison geneticist and horticulture professor Phil Simon recently published a study in the journal Nature Genetics detailing the first complete decoding of the carrot genome.

By studying the root vegetable's 32,115 genes, they were able to determine what caused formerly white carrots to become the bright orange snacks we know today. We can thank a gene called DCAR_032551 (also referred to as the carrot's Y gene), which plays an essential role in the accumulation of carotenoids, a class of natural pigments, in the carrot taproot.

"As well as sequencing the carrot genome we also studied specific genes, in particular part of the genome that includes the Y gene," Simon told Australia's ABC News. "We found that the Y gene accounts for the accumulation of orange and yellow carotenoid pigments in carrot roots."

The beta-carotene pigment naturally occurs in plants and fruits and is converted into vitamin A by the body. It is also found in foods like broccoli, spinach, and tomatoes, but it is the high concentration in carrots that accounts for the color. This is why consuming too many carrots or other beta-carotene rich foods can lead to carotenemia, a condition categorized by an increase of the pigment in the blood and skin discoloration.

According to the study, when carrot crops were first cultivated 1100 years ago in central Asia they were either purple or yellow (the original, wild carrot ancestors were white). Reliably orange carrots came later, around 1500 CE, and the pigment build-up was a "defect in a metabolic pathway that appears to be related to light-sensing," according to the researchers. They're not sure why planters favored certain carrot colors over others (the pigment does not affect the taste), but the intentional selection of the most orange (and thus more nutritious) carrots over the past four decades has resulted in crops that have 50 percent more carotene than they did in 1970.

[h/t Discovery]