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Scientists Unravel Genome of the Cow

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As a practical matter, having the genome is also going to make cattle breeding faster and cheaper.

Traits carried by bulls are important in determining how much milk a cow produces. Because bulls don't make milk, however, a bull's "performance profile" has to be sketched by observing the milk production of his daughters -- a process that takes about six years and costs $25,000 to $50,000. Now, male calves can be tested at birth for milk-enhancing traits using gene-chip technology.

"It doesn't take a rocket scientist to see that makes sense both logistically and financially," said Curt P. Van Tassell, a geneticist at the U.S. Department of Agriculture's laboratory in Beltsville, who was one of the leaders of the project.

There are two types of cattle -- taurine, which have no humps and predominate in Europe, Africa, the Americas and much of Asia; and indicine, which have humps and are in South Asia and East Africa. Both lineages descended from aurochs, a much larger and more aggressive species.

Indicine breeds have much greater genetic diversity than taurine breeds, evidence that they were developed from a larger number of "founder" animals.

Cows have a large number of genes devoted to big-gun, nonspecific defenses called "innate immunity," probably reflecting the fact that the animals rely on a huge variety of bacteria and other organisms to digest the roughage they eat.

"They need an immune system that can deal with that large microbial population in close proximity all the time," said Kim C. Worley, a geneticist at Baylor College of Medicine and one of the leaders of the project.

Both types of cattle show evidence of natural selection in genes that appear to be involved in making the animals -- large, horned and potentially dangerous -- docile. In some breeds, specific variants of behavior-related genes are "fixed," or seen in essentially every animal. Curiously, some of those genes are in regions that in the human genome seem to be involved in autism, brain development and mental retardation.


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