题干

现有两个非常大的某昆虫种群,个体间随机交配,无迁入和迁出,无突变,自然选择对A和a基因控制的性状没有作用。种群1的A基因频率为80%,a的基因频率为20%;种群2的A基因频率为60%,a%的基因频率为40%。假设这两个种群大小相等,地理隔离不再存在,两个种群完全合并为一个可随机交配的种群,则下一代中Aa的基因型频率是(   )

A:75%

B:50%

C:42%

D:21%

上一题 下一题 0.0难度 选择题 更新时间:2014-04-23 03:45:28

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C

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    Pocket Tape-Recorders “Family and Home Magazine” test what's on the market now.

1)Pearlcorder S702 $64

    This simple model at the bottom of the Olympus range scored the most points for its excellent quality of recording. Background noise hardly affects the sound and recording from a pocket is perfectly possible, but it doesn't turn off automatically.

Tape length: 30 minutes per side. Weight:240g.

2)Sony M9 $49.95

    Small and very good looking, sony's latest offering scored most for appearance. Sounds clear, but there is slight machine noise. The big control buttons are a great improvement on some of the complicated little controls on other tape-recorders. Doesn't switch off automatically but a red light shows if the machine is still running.

   Tape length: 60 minutes per side. Weight: 195g.

3)Sony M400 $115

    Lots of little control buttons that make a noise and are difficult to use . Recording was good but machine noise lost points. Tape counter and automatic switch-off when tape has finished recording or rewinding are useful Tape length: 60 minutes per side. Weight: 230g.

4)Imperial OEM. MC $29.95

    Cheap and simple compared with the rest, but recording was good as long as there was no background noise. Use only its own make of cassette. No light to show it is on; no fast forward button and the record button makes a loud noise.

    Tape length: 30 minutes per side. Weight: 285g.

5)Philips 585 $80

    Handsome and simple to use, but recording is very poor at more than the recommended distance of 5 cm-designed for dictation. No recording light. Tape length: 15 minutes per side. Weight: 220g.