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SourceResearchers at UT Southwestern Medical Center at Dallas have used canine DNA to identify a genetic mutation mechanism they believe is responsible for rapid evolutionary changes in the physical appearance of many species...
Most scientists agree that over very long periods of time, mutations in the genetic code are responsible for driving evolutionary changes in species. One widely accepted hypothesis is that random, so-called single-point mutations - a change from one letter to another among the billions of letters contained in the code - minutely but inexorably change an organism's appearance.
UT Southwestern scientists, however, believe the single-point mutation process is much too slow and happens much too infrequently to account for the rapid rise of new species found in the fossil record, or for the rapid evolutionary changes occurring in species such as the domestic dog, whose various breeds have evolved relatively quickly from a not-too-distant common ancestor...
The researchers found a correlation between the length and angle of the dogs' noses and specific regions in their genetic code that are prone to mutate often.
These genetic regions, called tandem repeat sequences, consist of the same series of letters repeated many times over, for example, A-C-T-A-C-T-A-C-T. Mutations happen in these regions when such units - the A-C-T in the above example - are mistakenly added or subtracted by the proteins responsible for \"reading\" and \"copying\" the letters in the genetic instructions. Such additions or deletions can result in changes in the proteins made by cells, which then affects how the cells function and, over time, the physical appearance of an animal. The researchers found that in a dog gene involved in determining muzzle length, the number of times specific tandem repeat units were repeated could be used as a predictor of what the dog looked like - long muzzle or short...
Mutations in tandem repeat sequences occur much more frequently than single point mutations - up to 100,000 times as often - and are much more likely to result in significant morphological changes, or changes in physical appearance, in an organism, said Dr. Fondon, an evolutionary biologist
