新視野大學(xué)英語(yǔ)視聽(tīng)說(shuō)教程第四冊(cè) Unit 8 Task 2: The Improvement of Rice

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Scientists now know a lot more about a grain that people have eaten for ten thousand years. (S1) Research teams around the world have completed a map of the (S2) genes of rices. The findings appeared last week in the (S3) journal Nature.

The aim is to speed up the improvement of rice. The scientists (S4) warn that the kinds of rice plants used now have reached the limit of their (S5) productivity. Yet world rice production must (S6) grow by an estimated 30 percent in the next twenty to meet demand. By 2025, as many as 4.6 billion people will depend on rice for (S7) survival. There is a lot of pressure on breeders to improve the crop, and the rice genome is a valuable tool to do that. (S8) Plant breeders have already used preliminary information from the rice genome to create experimental strains of rice that better resist cold and pests.

The researchers also say rice is an excellent choice for genetic mapping and engineering. Rice genes have only about 390 million chemical bases. That maight sound like a lot. But other major food grains have thousands of millions. (S9) The new map could better explain more than just rice. Rice shares a common ancestor with other cereal crops. Because rice is the first cereal crop to be fully analyzed, researchers expect that sufficient knowledge of its genetic information will reveal the heredity of more complex grains, including corn, wheat and barley.

(S10) While significant progress has been made in the analysis of the rice genome, the mapping of human genes is also making headway. When scientists can identify and manipulate genes that cause certain diseases, mankind will cure them easily. The human genetic map may help us control a person’s height, weight, appearance and even length of life.