Tandem repeats of sequences in developmental genes may contribute to morphological evolution, according to a paper in this week's PNAS. John W. Fondon, III, and Harold R. Garner of the University of Texas, Southwestern, show that different lengths of coding repeats in dogs correlate with morphological differences in the dogs' skulls and limbs. They also show that many other animals—including humans—have similar repeat length variation in their developmental genes.

The paper "seems to give a functional meaning to a kind of variation that we knew existed for a long time," Günter Wagner of Yale University told The Scientist. But "there was the possibility that this was just a form of evolutionary junk," said Wagner, who was not involved in the study.

Fondon and Garner sequenced tandem repeats from 92 breeds of dogs. They chose 37 repeat sequences from 17 canine developmental genes, mostly transcription factors. They found...

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