问题 单项选择题

某植物群体基因型的种类和比例为AA:Aa:aa=1:4:1,比较自交一代与随机交配一代得到的两个子代群体()。

A.基因型频率相同

B.纯合子比例不同

C.基因频率不同

D.杂合子比例相同

答案

参考答案:B

解析:

在一个足够大的种群中,如果不存在突变和自然选择,自交和随机交配产生的后代中,基因型频率不同。如Aa种群自交多代,纯合体AA和aa的频率逐渐升高,而杂合体Aa的频率逐渐降低。

问答题
阅读理解

Because of the financial crisis in the US and UK, college students are beginning to struggle to find ways to pay their tuition fees and accommodations.

Recently, two major US student loan lenders — Citibank and JPMorgan Chase — announced they were leaving the student loan industry altogether. Because banks currently have a lack of credit, they are reluctant to offer students low-interest loans that need a several-year wait for any return of interest.

In the US, many undergraduates top up their financial needs with a private loan, although the majority can get government-funded loans. In the 2005­-2006 academic year, $17 billion in private student loans was used to finance higher education. The shortfall in private funding has yet to be covered and will hit many US students hard.

Across the Atlantic, UK students have been less troubled by the crisis. Most undergraduates in the UK cover their university expenses with government-funded loans and grants (助学金). Their biggest concern is a sudden steep increase in student rent.

Most young professionals now rent houses, since 80 percent of UK mortgage schemes (住房抵押贷款计划) have disappeared — a direct result of the credit crisis. This has boosted the house rent market.

In large cities, UK students are paying almost 6.5 percent more in rent than the previous year. Figures from the UK organization Accommodation for Student show students in big cities such as London paying an average weekly rent of £103. Yet, despite students’ suffering, the number of this year’s university applications is expected to grow. During economic slumps (经济萧条时期), people regard further education as a way to survive tough job markets.

小题1:According to the passage, banks are unwilling to offer students loans because ________.

A.the students are poor and sometimes they can’t pay off the debt

B.banks prefer lending the money to the young professionals

C.banks don’t have enough money left at the present time

D.they think college students are not studying hard小题2:The underlined phrase “top up” in Paragraph 3 probably means ________.

A.put up

B.make up

C.fill up

D.pick up小题3:Which of the following is NOT true according to the passage?

A.UK college students have to pay more if they want to rent houses.

B.More UK students want to further their study in college.

C.It is not so easy for US students to loan money now.

D.College students’ tuition fees have risen greatly.小题4:It can be inferred that ________.

A.there are no private student loan lenders in the UK

B.loans for US college students will be increased next year

C.private funding falls a little because of higher-interest loans in the US

D.private loans play a very important role in financing US students’ education