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For years, scientists couldn't find the clue that determined why and how tigers and zebras got their stripes. It was only in a recent study that Harvard researchers brought together a range of mathematical models into a single equation. It determined the variables that could finally control these natural patterns.

"We wanted a very simple model in hopes that it would be big picture enough to include all of these different explanations," Tom Hiscock, lead author and Ph.D. student in Sean Megason's systems biology lab at Harvard Medical School, explained in a news release. "We now get to ask what is common among molecular, cellular, and mechanical hypotheses for how living things orient the directions of stripes, which can then tell you what kinds of experiments will (or won't) distinguish between them."

The mathematical models for these stripes were not too difficult to model. They found that tigers have parallel stripes, which are evenly spaced and perpendicular to the spine. They emerge when "interacting substances create waves of high and low concentrations of a pigment, chemical, or type of cell," according to natureworldnews.

Still, they could not discover how these stripes get oriented into one direction. So Hiscock and his team explored the issue.

Researchers have discovered that just one small change in the model can determine whether stripes are vertical or horizontal Still, they do not understand how it translates to living things.

 "We can describe what happens in stripe formation using this simple mathematical equation, but I don't think we know the nitty-gritty details of exactly what molecules or cells are mapping the formation of stripes," Hiscock said, adding that genetic mutants exist that can't form stripes or make spots instead, such as in zebrafish, but "the problem is you have a big network of interactions, and so any number of parameters can change the pattern."

Hence, the researchers created a "master model" to forecast three kinds of problems that might impact stripe orientation. Firstly, they might predict a change in "production gradient." This translates into a substance amplifying stripe pattern density. Secondly, they could follow "parameter gradient," in which any substance could alter any of the parameters that form the stripe. Finally, a physical change in the direction of the "molecular, cellular, or mechanical origin" of the stripe might also result in a change in the gradient.

Do these theories hold water? They need to be verified further to see whether the calculations hold true for living systems.

The study was published in the journal Cell Systems.