题干

用纯合的二倍体水稻品种高秆抗锈病(DDTT)和矮秆不抗锈病(ddtt)进行育种时,一种方法是杂交得到F1,F1再自交得到F2;另一种方法是用F1的花粉进行离体培养,再用秋水仙素处理幼苗得到相应植株.下列叙述正确的是(  )

A:前一种方法所得的F2中重组类型、纯合子各占 58 、 14

B:后一种方法所得的相应植株中可用于生产的类型比例为 23

C:前一种方法的原理是基因重组,原因是非同源染色体自由组合

D:后一种方法的原理是染色体变异,是由于染色体结构发生改变

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C

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    Chiang Mai is proud of the city's 700- year history, which has rich traditional relics and unique culture. It is located 700 km north of Bangkok and is situated among the highest mountains in the country. Chiang Mai means “the new city” in Thai. King Mengrai founded the city as the capital of the Lanna Kingdom on April 12,1296. Therefore, Chiang Mai not only became the capital and cultural center of the Lanna Kingdom, but was also to be the center of Buddhism in northern Thailand. King Mengrai , a very religious leader, founded many of the city's temples (寺庙) that remain important today.

    It is one of the few places in Thailand where it is possible to experience both historical and modern Thai Culture. The city has old temples next to modern stores. It has more than three hundred temples, among which some are the most beautiful and honorable in the entire Buddhist world, giving the city an atmosphere (氛围) of calmness.

    The old city of Chiang Mai has various dialects, architecture, traditional values, festivals, handicraft and classical dances. In addition, it has hill tribes and their wealth of unique culture. Chiang Mai city features old-world beauty and charm as well as modern enjoyment and convenience. It is also filled with natural resources including mountains, waterfalls and rivers. Nowadays there are many activities and attractions both in the city and the surrounding province, including river rafting , elephant riding and golf.

    The quality of living is excellent. Accommodation and food are of the highest standard at a very low cost. Entertainment is plentiful with numerous festivals, outdoor activities and great nightlife. A number of elephant camps, numerous outdoor activities, a variety of handicraft workshops, various cultural performances, and breathtaking scenery make Chiang Mai one of Asia's most attractive tourist destinations.