Magazine article Science News

Birds: Lightweights in the Genetic Sense

Magazine article Science News

Birds: Lightweights in the Genetic Sense

Article excerpt

Birds are the star athletes of the vertebrate world, pushing their bodies to metabolic extremes in order to defy gravity. Evolution has given them an edge by creating a lightweight skeleton, an aerodynamic coat of feathers, and a highly efficient respiratory system.

Their advantages even extend to the molecular realm. According to a new study, birds cast off excess genetic baggage long ago and in the process developed a much leaner genome.

Biologists have long known that bird cells contain less DNA than those of reptiles, mammals, and amphibians. But they did not know where the genetic differences lay. Austin L. Hughes and Marianne K. Hughes of Pennsylvania State University in University Park explored that question by comparing the sequences of 31 equivalent genes in humans and chickens--two animals for which this information exists.

They found that all of the chickens' sequences were shorter because they contain shorter introns, the regions of genes that contain so-called nonsense, or noncoding, DNA. Exons, the regions that contain the blueprints for protein formation, were roughly the same size in chickens and humans, the scientists report in the Oct. 5 Nature.

A single genetic change could not have shortened all chicken introns, the researchers argue. Instead, evolution gradually trimmed avian DNA, perhaps as an adaptation for flight.

Because the typical cell size of an animal tends to match the length of its genome, the development of shorter introns could account for the relatively small size of bird cells. …

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