问答题 果蝇中P因子的转座酶由4个外显子（0，1，2，3）编码。此基因在生殖细胞中的转录产物长度为2．1kb，包含所有这4个外显子，并编码具有转座酶活性的蛋白质。体细胞中P因子的转录产物长度为2．5kb，除了含有全部的4个外显子之外，位于外显子2和3之间的内含子也被保留下来。（1）体细胞中产生的较长的mRNA编码的蛋白质的大小只相当于在生殖细胞中产生的较短的转录产物编码的蛋白质的75％。较长的转录产物为什么会编码较小的蛋白质产物？（2）反转录酶能够用来从mRNA合成得到相应的双链DNA，这个DNA拷贝称为cDNA。如何利用cDNA和转基因技术得到在体细胞中也有转座酶活性的果蝇？（3）假设用限制酶SaZ工消化P因子后得到8个片段。用来自果蝇生殖细胞的转座酶的cDNA作为探针对它们进行Southern杂交，结果发现所有的8个限制酶切片段都显示阳性条带。上述结果说明了什么？

未知题型 数量遗传学家高尔登比较了男大学生和他们父亲的身高，得到以下结果： 所有父亲的平均身高与所有儿子的平均身高一致，但是对每一对父子而言，两人身高所属的类别(如较高或较矮)却并不一定一致。也就是说，最高的父亲可能有较矮的儿子，而很矮的父亲则可能有较高的儿子。由此得到的最优直线的斜率是0．67(实线)，而不是1．00(虚线)。高尔 登用“回归”(regression)一词来描述这种趋势，即儿子的表型比其父亲的表型更接近群体平均值。 (1)对回归现象作出解释。 (2)在此，回归与遗传率有什么关系?

单项选择题 London's First Light Rail System The Docklands Light Railway (DLR) took just three years to build at a cost of ￡77 million. It is London's first Light Rail System, but its route follows that of a number of older lines, which carried the nineteenth century railways through the crowded districts of the East End.The section of the line from the Tower Gateway Station to Poplar follows the line of one of London's earliest railways, the London & Blackwell (1840), a cable-drawn railway (later converted to steam) which carried passengers to steam ships at Blackwell Pier, and provided transport for the messengers and clerks who went backwards and forwards between the docks (码头) and the city every day.From Poplar to Island Gardens, a new line crosses high above the dock waters, and then joins the old track of the Millwall Extension Railway, built to service the Millwall Docks (1868) and to provide transport for workers in the local factories. This line was horse-drawn for part of its route, until the 1880s.The Poplar to Stratford section of the DLR route was first developed by the North London Railway, built in the 1850s to link the West and East India Docks with the manufacturing districts of the Midlands and North of England. There were major railway works and sidings (分线) at Bow until recently.The trains are automatically controlled from a central computer, which deals with all signaling and other safety factors, as well as adjusting speeds to keep within the timetable; on board each vehicle, Train Captains, who are also fully qualified drivers, are equipped with two-way radios to maintain contact with central control. There are passenger lifts, and self-service ticket machines, at every station. 第 41 题 The passage tells us that London's first Light Rail SystemA．was constructed in the nineteenth century.B．will be finished in three years' time.C．follows some of the original lines.D．took three years longer than expected to complete.