HOW did the leopard get its spots? How did the zebra get its stripes? The answer may be a gene, which scientists have found governs colour patterns in deer mice, the most widespread mammal in North America. This gene, called Agouti, is found in all vertebrates and may establish colour pattern in a wide variety of species, a process that has been poorly understood at both the molecular and the evolutionary level. "The question of how colour patterns are established in vertebrates has been a black box," said Marie Manceau, a research associate in Harvard University's Department of Organismic and Evolutionary Biology and lead author. "Taking advantage of the simple colour pattern of deer mice - which have a dark back and a light belly - we showed that small changes in the activity of a single pigmentation gene in embryos generate big differences in adult colour pattern," she added. Manceau and senior author Hopi E. Hoekstra found that colour patterns in these mice rely on the establishment of an embryonic 'pre-pattern' of Agouti expression. In the mice they studied, this took place midway through gestation - just 12 days after conception, well before the first pigments are ever produced in the skin. Researchers already knew that Agouti affects how deeply adult fur is shaded. But the latest research found that subtle changes in the gene's embryonic activity could also make a profound difference in the distribution of pigments across the entire body. "During embryogenesis, Agouti is expressed in the belly, where it delays maturation of the cells that will eventually produce pigments," said Hoekstra. "This leads to a lighter colored belly in adults, which is the most common color pattern across a wide variety of vertebrates, from fish to antelope," he added. Sify