题干

在DNA 测序工作中,需要将某些限制性内切酶的限制位点在 DNA上定位,使其成为 DNA 分子中的物理参照点。这项工作叫做“限制酶图谱的构建”。假设有以下一项实验:用限制酶 HindⅢ,BamHⅠ和二者的混合物分别降解一个 4kb(1kb即1千个碱基对)大小的线性DNA 分子,降解产物分别进行凝胶电泳,在电场的作用下,降解产物分开,如下图所示。

据此分析,这两种限制性内切酶在该DNA 分子上的限制位点数目是以下哪一组?

A:HindⅢ1个,BamHⅠ2个

B:HindⅢ2个,BamHⅠ3个

C:HindⅢ2个,BamHⅠ1个

D:HindⅢ和BamHⅠ各有2个

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答案(点此获取答案解析)

A

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    Two young giant-panda twins born in the United States have returned home to China, but are straggling to adapt to the language and food.

    The 3-year-old sisters, Mei Lun and Mei Huan, wens the first surviving panda twins to be born in the United States, and were returned to China from Zoo Atlanta on Nov. 5. But the pair still understand English belter than Chinese, and prefer American biscuits to Chinese bread.

    A zoo-keeper said that his main concern is that the pair are so addicted to American biscuits that everything they eat — from bamboos to apples — has to be mixed with biscuits. They even want to snack on (零食) biscuits when drinking water.

    The zoo -keeper is trying to wean them off their biscuit habit, gradually replacing the American food with Chinese bread. Mei Huan is adapting, but Mei Lun doesn't want to touch the unfamiliar bread.

    Mei Lun is the livelier of the two, often jumping onto the roof and hanging upside down from a rail, but her slightly younger sister Mei Huan is calmer, preferring to sit still, observe her new environment and occasionally snack on bamboo.

    A language barrier is also reported. While the pair respond to their own names, and understand some English phrases such as “come here,” they don't understand the Sichuan dialect of Chinese.

    The news caused some laughter on Chinese social media, with some users commenting that the pandas would soon get used to Sichuan's famously spicy cuisine.