一 群体改良的意义 1 群体改良（Population Improvement）：通过对被改良的群体进行周期性选择、 重组来逐渐提高群体中有利基因和基因组合的频率，以改进群体表现的方法。
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maize population improvement 玉米群体改良
wheat population improvement 小麦群体改良
maize population improvement in china 玉米群体改良
Improvement of population policy 人口政策的完善
Dan988 was bred in 1989 by using hybrid PN78599 as the basic material with the methods of self cross, N-ion radiation, big population improvement,characters directed transferring technology and so on.
玉米自交系丹988是以引入美国"PN78599"杂交种为基础材料,经自交、N离子辐射处理、大群体改良、性状定向转育等技术方法选育而成。
参考来源 - 优良玉米自交系丹988创新选育方法研究·2,447,543篇论文数据，部分数据来源于NoteExpress
A grey recurrent population improvement of wheat was suggested by combining the grey breeding method with the wheat dwarf male-sterile technology.
将灰色育种方法与矮败群体改良方法相结合，提出了小麦灰色轮回群体改良方法。
Where salt iodization has been in place for at least a year, improvement in iodine status within the population has been overwhelming.
在食盐碘化已至少进行一年的地方，人群中的碘状况已取得确凿的改善。
The slowest improvement has been in the WHO African Region, where the percentage of the population using toilets or latrines increased from 30% in 1990 to 34% in 2008.
世卫组织非洲区域在这方面进展最为缓慢，到2008年，使用厕所的人口比例从1990年的30%仅增加到34%。
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