This picture has been making the rounds of the internet for a couple of years now. It was provided by the Center of Natural Sciences in Prato, Italy, Wednesday, June 11, 2008, and shows a deer with a single horn in the center of its head. The one-year-old roe deer - nicknamed 'Unicorn' - was born in captivity in the research center's park in the Tuscan town of Prato, near Florence, Gilberto Tozzi, director of the Center of Natural Sciences, said. Since his twin has two horns, it is easy to explain what happened here.
Don't expect to find herds of unicorns spawned by this little buck when he matures. His offspring, if he is allowed to mate, will very likely be normal and have two horns. This is what is called a mosaic mutation. It is like the case of someone being born with one blue eye and one brown eye or a blond streak in an otherwise dark head of hair.
There are a whole lot of genes in our makeup that are read-only. There aren’t really any options or variants. These genes make up about 97% of our entire genome and are the ones that make us human—you know, two arms, two legs, head on top, feet, hands, two eyes, stomach in the middle, those kinds of things. They are the genes that make the little roe deer a roe deer instead of human or white-tailed deer or elephant or puppy. Those are hard-wired in and don’t regularly change. That goes for the two horns or antlers on the head genes.
When we see a change in expression of a trait that is part of the make-up of an organism, it is usually a mosaic mutation. A mutation that will not be passed along to the next generation, a mutation that comes about AFTER the egg is fertilized and is a result of some environmental factor during the development of the embryo/fetus. This includes such things as birth defects caused by heavy smoking or drinking or drug use on the part of the mother. It also includes drinking polluted water or breathing polluted air or being subject to such things as radiation while the embryo is developing.
When we see a change in expression of a trait that is part of the make-up of an organism, it is usually a mosaic mutation. A mutation that will not be passed along to the next generation, a mutation that comes about AFTER the egg is fertilized and is a result of some environmental factor during the development of the embryo/fetus. This includes such things as birth defects caused by heavy smoking or drinking or drug use on the part of the mother. It also includes drinking polluted water or breathing polluted air or being subject to such things as radiation while the embryo is developing.
A mosaic mutation may also occur when some external force comes to bear on the development of the embryo. The genetic blueprint calls for two horns, one on each side of the top of the head of the deer. Early in the development of the embryo, while the decisions are being guided by the enzymes and proteins made by the DNA a force—perhaps a physical force inside the womb causes one of the horns not to develop. This happens quite frequently; however, what doesn’t happen so frequently is that the force also pushes the budding horn over toward the middle of the head so the single horn grows right out of the middle of the front of the skull. In that case, you get this guy named, Unicorn.
His genes told the developing cells to produce two horns, but something prevented it. The genes he will pass on to the next generation will have instructions for two horns, one on each side just like “normal.”
Earlier I said, “If he is allowed to mate.” I said that because nature is pretty set on keeping things as is. The females may choose not mate with a male who is so different. Cruel? Maybe from the “Bambi” point of view, humanizing the deer that is, it might seem cruel, but nature is rather unforgiving. Adapt or die. Predators take out the sick and the weak, the odd are not allowed to mate. This keeps the species strong.
--klock
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