题干

关于生物进化趋势的表述中,不合理的是(    )

A:低等生物→高等生物

B:体型小的生物→体型大的生物

C:结构简单→结构复杂

D:单细胞生物→多细胞生物

上一题 下一题 0.0难度 选择题 更新时间:2020-03-23 03:44:15

答案(点此获取答案解析)

B

同类题2

水稻叶片宽窄受细胞数目和细胞宽度的影响,为探究水稻窄叶突变体的遗传机理,科研人员进行了实验.

(1)科研人员利用化学诱变剂处理野生型宽叶水稻,可诱发野生型水稻的DNA分子中发生碱基对的____ ,导致基因突变,获得水稻窄叶突变体.

(2)测定窄叶突变体和野生型宽叶水稻的叶片细胞数目和单个细胞宽度,结果如右图所示.该结果说明窄叶是由于____ 所致.

(3)将窄叶突变体与野生型水稻杂交,F1均为野生型,F1自交,测定F2水稻的____ ,统计得到野生型122株,窄叶突变体39株.据此推测窄叶性状是由____ 控制.

(4)研究发现,窄叶突变基因位于2号染色体上.科研人员推测2号染色体上已知的三个突变基因可能与窄叶性状出现有关.这三个突变基因中碱基发生的变化如表所示.

突变基因

碱基变化

C→CG

C→T

CTT→C

蛋白质

与野生型分子结构无差异

与野生型有一个氨基酸不同

长度比野生型明显变短

由上表推测,基因Ⅰ的突变没有发生在____ 序列,该基因突变____ (填“会”或“不会”)导致窄叶性状.基因Ⅲ突变使蛋白质长度明显变短,这是由于基因Ⅲ的突变导致____ .

(5)随机选择若干株F2窄叶突变体进行测序,发现基因Ⅱ的36次测序结果中该位点的碱基35次为T,基因Ⅲ的21次测序结果中该位点均为碱基TT缺失.综合上述实验结果判断,窄叶突变体是由于基因____ 发生了突变.

(6)F2群体野生型122株,窄叶突变体39株,仍符合3:1的性状分离比,其原因可能是____ 

同类题4

阅读理解

    Driving in Canada is similar to driving in many parts of the United States. Distances and speeds, however, are posted in kilometers per hour and some signs, particularly in Quebec, may only be in French.

    Unless otherwise posted, the maximum (最大限度的) speed limit in Canada is 50km/hr in cities and 80km/hr on highways. On rural highways, the posted speed limit may be 100km/hr. It is illegal to take automobile radar detectors (汽车雷达检测器) into Quebec, Ontario, Manitoba, and the Yukon. Seat belt use is required by law for all passengers, and child car seats must be used by children under 40 pounds. Some provinces require drivers to keep their vehicles' headlights on during the day and some have banned (禁止) driving while using a hand-held cell phone. Motorcycles cannot share a lane (车道), and safety helmets for motorcycle riders and passengers are necessary. Running a red light is a serious crime throughout Canada and drivers are advised to stop before starting when a light turns green.

    Winter travel can be dangerous due to heavy snowfalls and icy conditions. Some roads and bridges are often closed in winter. Snow tires are required in some provinces. Travelers should also be careful about animals while driving at night in rural areas.

    Highway 401, from Detroit to Montreal, is one of the busiest highways in North America. It has been the scene of many deadly traffic accidents due to sudden and severe weather changes, high rates of speed, and heavy truck traffic. Thus drivers should be alert while travelling here.

    Please refer to our Road Safety page for more information. Also, we suggest that you visit the website of Canada's national authority responsible for road safety.