| 第 1 页：听力原文 |
| 第 2 页：全文参考译文 |
| 第 3 页：词汇讲解 |
| 第 4 页：词组及语法讲解 |
| 第 5 页：长难句讲解 |
This is the VOA Special English Agriculture Report.
Researchers from twenty-five countries have made a genetic map of a cow. Better understanding of what makes a cow a cow could lead to better milk and meat production. It could also help the drug industry.
The Bovine Genome Sequencing Project found that the cow genome contains at least twenty-two thousand genes. Most of these are shared among humans as well as mice, rats and other mammals used for comparison.
Mice and rats are commonly used to test new medicines. But the study shows that cows are more similar to humans than to mice or rats.
Project scientist Harris Lewin from the University of Illinois at Urbana-Champaign predicts there will be more laboratory cows in the future. He says during evolution millions of years ago, domesticated cattle separated from a common ancestor that led to humans.
The new findings are in the journal Science. More than three hundred researchers studied a female Hereford cow from the American state of Montana. The genetic map, or genome, took six years to complete.
A related report looked at genetic changes in cattle over time. More than two hundred fifty thousand years ago, the bovine family tree divided into two major groups.
Taurine cattle have no hump on their back. They are most commonly found in Europe, Africa and East and West Asia, as well as the Americas. Indicine cattle have a hump and are found in India, South and West Asia and East Africa.
Humans started to domesticate wild cows about eight to ten thousand years ago. Scientists examined several breeds and say the cattle genome appears to show evidence of this selective reproduction.
Today there are more than eight hundred breeds of cattle raised for different reasons. But some people are concerned that breeding has reduced genetic differences among cattle. This could make it easier for disorders to affect a large number of animals.
The scientists say the current level of diversity within cattle breeds is at least as great as within humans. And they say the new genome will make it possible to better protect genetic diversity.
Yet there may be more questions to settle about what exactly makes a cow a cow. A team led by Steven Salzberg from the University of Maryland also published a cow genome last month in the journal Genome Biology. That team disagreed on some points with the findings in Science.
And that's the VOA Special English Agriculture Report, written by Jerilyn Watson.
