问题 问答题 简答题

何为基因对基因学说?

答案

参考答案:

针对寄主植物的每一个抗病基因,病原菌迟早会出现一个相对应的毒性基因;毒性基因只能克服其相应的抗性基因,而产生毒性(致病)效应。

在寄主-寄生物体系中,任何一方的每个基因都只有在另一方相应基因的作用下,才能被鉴定出来。假定抗病基因是显性,无毒基因是显性,只有当抗病基因与对应的无毒基因匹配时,寄主才表现抗病反应,其他均为感病反应。

单项选择题
单项选择题

European farm ministers have ended three weeks of negotiations with a deal which they claim represents genuine reform of the common agricultural policy (CAP). Will it be enough to kick off the Doha world trade negotiations

On the face of it, the deal agreed in the early hours of Thursday June 26th looks promising. Most subsidies linked to specific farm products are, at last, to be broken--the idea is to replace these with a direct payment to farmers, .unconnected to particular products. Support prices for several key products, including milk and butter, are to be cut-that should mean European prices eventually falling towards the world market level. Cut-ting the link between subsidy and production was the main objective of proposals put forward by Mr. Fischler, which had formed the starting point for the negotiations.

The CAP is hugely unpopular around the world. It subsidizes European farmers to such an extent that they can undercut farmers from poor countries, who also face trade barriers that largely exclude them from the potentially lucrative European market. Farm trade is also a key feature of the Doha round of trade talks, launched under the auspices of the World Trade Organization (WTO) in November 2001. Developing countries have lined up alongside a number of industrial countries to demand an end to the massive subsidies Europe pays its farmers. Several Doha deadlines have already been missed because of the EU’s intransigence, and the survival of the talks will be at risk if no progress is made by September, when the world’s trade ministers meet in Cancun, Mexico.

But now even the French seem to have gone along with the deal hammered out in Luxembourg. Up to a point, anyway. The package of measures gives the green light for the most eager reformers to move fast to implement the changes within their own countries. But there is an escape clause of sorts for the French and other reform-averse nations. They can delay implementation for up to two years. There is also a suggestion that the reforms might not apply where there is a chance that they would lead to a reduction in land under cultivation.

These 1et-outs are potentially damaging for Europe’s negotiators in the Doha round. They could significantly reduce the cost savings that the reforms might otherwise generate and, in turn, keep European expenditure on farm support unacceptably high by world standards. Mote generally, the escape clauses could undermine the reforms by encouraging the suspicion that the new package will not deliver the changes that its supporters claim Close analysis of what is inevitably a very complicated package might confirm the sceptics’ fears.

In what case might the escape clauses apply in reform-averse nations()

A. Farmers lose their interest in farming

B. Reforms have to be delayed for up to two years

C. Implementation of the measures goes too eagerly

D. The measures damage the reformers’ confidence