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生物进化的实质是种群基因频率的定向改变,其中影响种群基因频率的因素有很多,如自然选择,…等.某中学一个研究小组为探究人工选择对种群基因频率的影响,选用了纯种长翅果蝇和残翅果蝇进行实验.已知果蝇的长翅(B)对残翅(b)为显性,基因位于常染色体上.他们的实验过程如下:

•选择一只纯种雄性长翅果蝇与一只残翅雌性果蝇进行杂交,获得子一代雌雄果蝇;

•让子一代果蝇连续自由交配5代,同时在每一代中要除去残翅果蝇;

•当子六代所有长翅果蝇自由交配后,统计子七代长翅果蝇和残翅果蝇在种群中的百分比;

•根据残翅果蝇的百分比计算出B,b基因在种群中的基因频率,得出结论.

紫茎泽兰是一种恶性入侵杂草,该植物耐贫瘠,入侵后可迅速侵占撂荒地、疏林草地,排挤当地植物,给许多地区造成了严重的经济和生态损失.为研究其入侵机制,对某入侵地区进行了调查,结果如表:

调查项目

重入侵区

轻入侵区

未入侵区

植物覆盖度

紫茎泽兰覆盖度(%)

67.2

20.3

0

当地植物覆盖度(%)

3.1

45.8

52.5

土壤微生物

总真菌数(×104个)

17.9

5.8

8.3

固氨菌(×105个)

4.4

2.9

2.2

硝化细菌(×104个)

8.7

7.8

7.2

植物可吸收的无机盐

NO3﹣(mg/kg)

92.0

27.9

15.7

NH4+(mg/kg)

53.0

15.3

5.3

植物可吸收磷(mg/kg)

8.7

3.4

2.6

植物可吸收钾(mg/kg)

351.0

241.5

302.8

注:植物覆盖度是指某一地区植物茎叶垂直投影面积与该地区面积之比.

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    Last night, on my way home I stopped because of being attracted by some hamburgers at a fast food restaurant. On my way in, a homeless man approached me and asked, “Do you have any bottles lying around?” I knew he would recycle them for a few cents, but I didn't have any, so I said no. And again he asked, “Can you spare some change ?” I smiled, and said no again. He was very respectful; he smiled back and said, “OK, thank you.” Even though he didn't have anything, he was still in good spirits. From the way he spoke I could tell he was smart.

    Then I bought one hamburger and enjoyed my meal, but in the back of my mind I wondered whether the homeless man was hungry. After I finished my meal I decided to order another one for him. At this point I didn't know if he was still around, but I tried anyway.

    At the counter I ordered a hamburger and also a hot chocolate, because it was cold outside, and I thought it would help warm him up. They delivered me the hot chocolate first and as I waited for my hamburger, I noticed the homeless man was standing right beside me. I looked at him and smiled, “This hot chocolate is for you.” He replied like a gentleman, “Thank you so much. That's very kind of you.”

    I always believe no matter how hard up I am, there are always those who are worse off than I. When you help someone, it's not always about money, it's about love. The love you give today, someone might forget tomorrow. It doesn't matter. Love anyway, because the greatest thing you can give is love.