题干

一对等位基因控制着同一性状的不同表现类型(如豌豆中,基因D控制高茎,基因d控制矮茎),这是因为(  )

A:不同基因合成蛋白质的场所不同

B:等位基因分离的结果

C:不同基因中脱氧核苷酸的排列顺序不同

D:个体发育过程不同

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答案(点此获取答案解析)

C

同类题1

阅读下面的说明文段,回答下题。

3D 打印的革命性

       3D 打印源自100 多年前的照相雕塑和地貌成形技术,是一种不需要传统刀具和机床就能打造出任意形状、根据物体的三维模型数据制成实物模型的技术,被认为是一项改变世界的新技术。

       3D 打印使用的不是传统的“墨”,而是那些能发生固化反应的材料,比如树脂、塑料、陶瓷、金属等,因而能“打印”出实实在在的三维立体模型,就像童话中的“复制机”一般神奇。这将使工厂彻底告别车床、冲压机、制模机等传统工具,从而转变为一种以3D 打印为基础的成本更低、研发周期更短的生产方式。英国《经济学家》杂志曾刊发题为《第三次工业革命》的文章,称3D 打印标志着第三次工业革命的到来。以目前的发展情况判断,3D 打印之后,必将是社会制造业的迅猛崛起。

       据报道,国外目前已经通过3D 打印技术成功地“打印”出了自行车、汽车、电控飞行器等物。现今,3D 打印也应用于珠宝制造和模型制作,在时装业、电影业、建筑业等10 多个不同的行业显示出了十足的魅力,并大大改变了美国制造业的格局。其实,众多的3D 打印创业者此前早已落户以虚拟经济著称的纽约市,即便在2008 年金融危机的情况下,3D打印还是拉动了当地的萧条经济,为经济增长贡献了力量。

       3D 打印的应用并不止于工业制造,它在医学界也有着广阔的发展前景。如果它用来打印的“墨”是一个个活体细胞,那么,只要获得相关器官的切片数据,该器官就可以被“打印”出来。这并非天方夜谭,

       在去年举行的全球科技娱乐设计大会(TED)上,美国维克森林再生医学学院博士安东尼就向人们展示了这样一个肾脏模型打印的过程。。据他介绍,他们正在进行一个更大胆的试验,直接用打印机在人体伤口上进行修复式“打印”,如果取得成功,这将是医学领域的重大进展。

同类题4

阅读下面短文,从短文后各题所给的四个选项(A、B、C、D)中,选出可以填入空白处的最佳选项。

    People from every corner flooded into the streets that Christmas Eve. “Frosty the Snowman,” and “Jingle Bells” 1 in stores; on the pavements, the street singers performed happily. Everyone, was2 by someone else, delighted and cheerful. I was alone.

    As one of 8 kids of a Brazilian family, brought up in America's crowded apartment, I'd spent several years searching for aloneness. Now, 3, at 27, a college student after the 4 with my girlfriend , every cell inside me wanted to be alone, 5 not at Christmas. My family had 6 to Brazil and my friends were 7 with their own lives. Dusk was approaching, and the fact that I had to return to my 8 home made me sad. Lights from windows blinked, and I hoped someone would 9 from one of those homes to invite me inside with a Christmas tree decorated with shiny fake snow and 10 presents.

    At a market, I felt more 11 when people were buying lots of goods, which 12 the gifts we received as children in my mind . I missed my family and wanted to cry for wanting to be alone and for having achieved it.

    Outside the church , a manger(小耶稣) had been set 13. I stood with others watching the scene, some of them 14themselves, praying. As I walked home, I realized that leaving Brazil was still a painful experience as I struggled with 15 I had become in 15 years in America. I'd mourned the 16, but for the first time, I recognized what I'd gained. I was independent, 17 and healthy. My life was still ahead, full of 18.

    Sometimes the best gift is the one that you give yourself. That Christmas, I gave myself 19 for what I'd obtained up to now and promise to go forward. It is the best gift I've ever got, the one that I most 20.