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From Calico Cats to Humans

From an interview with Karen Cone, Professor of Biological Sciences


This research on DNA packaging is applicable to every organism, Cone observes. Using the example of a calico cat, she explains: “Tortoise-shell and calico cats have orange and black fur patches on their body. That is due to a DNA packaging phenomenon.” As it turns out, the fur color gene is on the X chromosome. Just as human females have two X chromosomes, so do these calico cats, which are almost always female. In fact, they have one X with an orange-fur gene and one X with a black-fur gene: “so back when that little calico cat, with her different X chromosomes, was a 16 or a 32-cell embryo, in each cell, one of the X chromosomes got really tightly packaged, so tightly that the genes on that chromosome weren’t expressed.” If the X with the orange-fur gene is packaged, she continues, then the X with the black-fur gene remains active. As the cell divides further in the embryo, it will eventually give rise to a black patch of fur. The orange patches, of course, derive from the fact that in another cell, the X with the orange-fur gene, was the one left active, while the black one was balled up too tightly to be expressed. That is one concrete example of how DNA packaging influences whether or not a gene is turned on.