问题 读图填空题

回答下列小麦杂交育种的问题:

(1)设小麦的高产与低产受一对等位基因控制,基因型AA为高产,Aa为中产,aa为低产。抗锈病与不抗锈病受另一对等位基因控制(用B、b表示),只要有一个B基因就表现为抗病。这两对等位基因的遗传遵循自由组合定律。现有高产不抗锈病与地产抗锈病两个纯种品系杂交产生F1,F1自交得F2

①.F2的表现型有_____种,其中能稳定遗传的高产抗锈病个体的基因型为______,占F2的比例为_____。

②.选出F2中抗锈病的品系自交的F3,请在上表中填写F3各种基因型的频率。

(2)另假设小麦高产与低产由两对同源染色体上的两对等位基因(A1与a1,A2与a2)控制,且含显性基因越多产量越高。现有高产与低产两个纯系杂交得F1,F1自交得F2,F2中出现了高产、中高产、中产、中低产、低产五个品系。

①.F2中,中产的基因型为_________。

②.在上图中画出F2中高产、中高产、中产、中低产、低产五个品系性状分离比的柱状图。

答案

(1)①.6     AABB    1/16        ②.BB=1/2    Bb=1/3     bb=1/6

(2)①.A1a1A2a2、A1A1a2a2、a1a1A2A2

②.

单项选择题

A rare provision in San Francisco’s business tax code that taxes companies when employees cash in their stock options has caused a stir in this hotbed of fledgling tech companies. Remarkably, few companies even knew about the tax, which has been in effect for seven years. But since city officials offered Twitter a payroll-tax break as an incentive for it to remain in San Francisco (the company is considered likely to go public soon), the stock-option provision has suddenly come under intense scrutiny. A number of other booming companies, including Zings, the maker of online games and one of the city’s fastest-growing firms, have threatened to leave the city unless they receive similar payroll-tax exemptions before going public.

Unlike most cities, San Francisco generates most of its business tax revenue through a payroll tax. The Twitter exemption bill, which will be considered by the full Board of Supervisors on April 5, would freeze payroll taxes for six years along a strip of Market Street—where Twitter is set to relocate—and several square blocks in the Tenderloin neighborhood. Twitter executives had been concerned because since 2004 the city’s payroll tax code has counted stock options granted to employees as compensation, which is taxed at 1.5 percent. If Twitter goes public in San Francisco and a large number of workers exercise their options, the city would tax the company on its employees’ stock gains—a bill likely to amount to tens of millions of dollars. "Twitter could be looking at a significantly larger payroll tax liability if and when it goes public," said Ted Egan, the chief economist in San Francisco’s controller’s office.

Because of the dearth of I. P. O. ’s inside the city limits in the last decade, the stockoption tax has gone under radar until now. Businesses, city officials and even seasoned tax lawyers are confounded. "Nobody ever talked about this because nobody’s really tested these issues before," said Thomas H. Steele, a partner in Morrison & Foerster’s San Francisco office, specializing in state and local tax. He said that his clients began calling him this week to ask about the tax’s ramifications. "A Pandora’s box has already been opened," said Supervisor Ross Mirkarimi, a member of the Board of Supervisors’ budget and finance committee, who has expressed concern about tailoring legislation for one company. "We’ve been going about this the wrong way," he said. The recent confusion has added impetus to calls for comprehensive business tax reform by David Chiu, the board president. "The stock option problem is real," Mr. Chiu said. "We have to address it in a fair and responsible way.

According to Ross Mirkarimi,which is Right()

A. Don’t give Twitter the tax-free policies

B. Changing the law for the companies is wrong

C. There would be more similar occurances to come out

D. He would veto at the meeting

实验题