题干

红眼(R)雌果蝇和白眼(r)雄果蝇交配,F1 全是红眼,F1 雌雄交配所得的F2中红眼雌果蝇121只,红眼雄果蝇60只,白眼雌果蝇0只,白眼雄果蝇59只.则F2卵中R和r及精子中R和r的比例是(  )

A:卵细胞:R:r=1:1,精子:R:r=3:1

B:卵细胞:R:r=3:1,精子:R:r=3:1

C:卵细胞:R:r=1:1,精子:R:r=1:1

D:卵细胞:R:r=3:1,精子:R:r=1:1

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答案(点此获取答案解析)

D

同类题2

阅读下文,回答问题。

大先生

    先生姓凌,有绝活儿,能把戏里的场景搬到木头上,一块巴掌大的破木板,只需半炷香的工夫,就能让人瞧明白刻的是“桃园三结义”还是“三英战吕布”。所以凌先生起初是凌木匠。

    凌木匠不是本地人,早年间逃荒来的。凌木匠来到村里的日子,是那年冬天日头最短的时候。薄暮下,先是一根打狗棍进了三叔家的院门,继而是一个身影,像用那根棍子挑进来的,破衣旧絮,褡裢挂在肩头,趿拉着一双单布鞋的脚,有一只似乎受了伤,缠着破布条。正在院里喂鸡的三婶,委实被吓着了,以为大白天撞到鬼。刚要喊人,“鬼”却先开口,怯生生地道:“大娘啊,要饭的来了,给口吃的吧。”三婶仔细一瞧,是个讨饭的。只见他端着搪瓷缸子的手捂在胸口,哀求就是从那里发出来的。给完吃的,三叔三婶看他可怜,天又冷,就留他在磨坊里过夜。凌木匠望着三叔三婶的眼睛,变得浑浊了。天亮后,他见磨坊里堆着打磨了一半的木料,知道这家要盖房。就对三叔说,他会做木工,可以帮忙,给口吃的就行。三叔寻思,正好雇的木匠有事,就让他试试吧。没想到,凌木匠的手艺精得很,不但会做门窗,还会木雕,窗棂花饰、门簪颂语,好看极了。就这样,凌木匠留在了我们村,成了凌先生。

    后来,村里人又知他不光有好手艺,还装着一肚子墨水。嘿,正好村里小学缺个先生。于是,他就成了凌先生。“手艺人”在村人口中格外尊贵,而凌先生的尊贵,一部分来自他的手艺,一部分来自肚子里的墨水。因此,“手艺人”和“先生”似乎都配不上凌先生了,村人便称他为“大先生”。

    大先生活儿细,字儿好,可闷头做活儿可以,写信作文也行,只是嘴太笨,肚子里的学问也便像茶壶里的饺子,倒不出来。而大先生就是理儿多,不光要讲个“知其然”,还要讲个“知其所以然”,于是越讲我们越糊涂。渐渐地,他就不受娃们待见,娃们老是捉弄他。

    大先生喜欢讲唐诗,尤其是李白的诗。“床前明月光,疑是地上霜。”大先生说李白的床不是床,而是井栏。说这话时,身为木匠的大先生显得颇有把握。我们却哄堂大笑,床就是床,怎么可能是井栏呢?每次我们一笑,他就一窘,嗓门提高了,像是要争辩,说:“你们想想,床在屋里,窗户是木头的,还贴着纸,哪会看得见月光?在院子里,就着月光,看到井栏,才会思乡,背井离乡嘛!”

    讲到这里,他突然停住了,扭头望着窗外,我们也停止了议论,只有窗外不知谁家的羊在不知趣地叫着。大先生陷入沉思,眼睛变得浑浊。然后。他又扭过头来,说:“这是思归之辞也!”教室里又是一片笑声,“死鬼之词”,大先生骂李白是个死鬼哩……不知从哪冒出来的灵感,我站起来说了一句:“就是想家了嘛!”大先生用浑浊的目光向我投来赞许之意,似乎还念叨了一句:“孺子可教也。”

    农村撤点并校后,大先生也退了。教了几十年的书,一下子闲下来,不知所措,于是,大先生又拾起了木匠活儿。让他想不到的是,国家针对民办教师的新政策出台后,给大先生补上了退休待遇。头次领到工资,他就跑到支书家里,说:“我教书时,每月不到300块,现在不教了,怎么还拿3000块呢?不能白拿这钱。”支书跟他掰扯了半天,也没讲明白,命令道:“国家的政策,不拿也得拿!”大先生的眼睛又浑浊起来。

    后来,大先生用每月领到的钱买了好多木料,做了结实的课桌椅,给镇上的学校送去。再后来,还设了助学会,村里谁家的孩子考上大学,他就赞助一笔。直到有一天,他心满意足地躺进自己打制的棺材。

   大先生死的那天,我特地查了《辞海》,其中一条写:“床,井上围栏。”

同类题4

阅读下列短文,从每题所给的四个选项(A、B、C和D)中,选出最佳选项。

    As Internet users become more dependent on the Internet to store information, are people remembering less? If you know your computer will save information, why store it in your own personal memory, your brain? Experts are wondering if the Internet is changing what we remember and how.

    In a recent study, Professor Betsy Sparrow conducted some experiments. She and her research team wanted to know the Internet is changing memory. In the first experiment, they gave people 40 unimportant facts to type into a computer. The first group of people understood that the computer would save the information. The second group understood that the computer would not save it. Later, the second group remembered the information better. People in the first group knew they could find the information again, so they did not try to remember it.

In another experiment, the researchers gave people facts to remember, and told them where to find the information on the computer. The information was in a specific computer folder (文件夹). Surprisingly, people later remember the folder location (位置) better than the facts. When people use the Internet, they do not remember the information. Rather, they remember how to find it. This is called "transactive memory (交互记忆)"

    According to Sparrow, we are not becoming people with poor memories as a result of the Internet. Instead, computer users are developing stronger transactive memories; that is, people are learning how to organize huge quantities of information so that they are able to access(获取) it at a later date. This doesn't mean we are becoming either more or less intelligent, but there is no doubt that the way we use memory is changing.