下列关于低温诱导染色体加倍实验的叙述，正确的是（）。
A．原理：低温抑制染色体着丝点分裂，使子染色体不能分别移向两极
B．解离：盐酸酒精混合液和卡诺氏液都可以使洋葱根尖解离
C．染色：改良苯酚品红溶液和醋酸洋红溶液都可以使染色体着色
D．观察：显微镜下可以看到大多数细胞的染色体数目发生改变
参考答案：C
解析：
低温会抑制纺锤体的形成，但是着丝点照常会分裂，使姐妹染色单体分裂形成子染色体，A项错误；解离液是由15%的盐酸和95%的酒精等体积混合而成，其作用是使细胞分散开来，改变细胞膜的通透性，而卡诺氏液的作用是固定细胞形态，B项错误；人教版必修二88页《低温诱导染色体数目变化》实验中用改良苯酚品红溶液使染色体着色，而人教版必修一115页《观察根尖分生组织细胞有丝分裂》实验中则是用醋酸洋红溶液使染色体着色，C项正确。正常情况下，只有在分裂后期才能看到染色体数目改变——加倍，但在显微镜下可以看到大多数细胞处于间期，而染色体变异导致的染色体数目的改变出现的可能性更低，D项错误。
| The basic story is very old indeed and familiar to most of us. The heroine, Cinderella, is treated cruelly by her stepmother and mocked by her two ugly stepsisters. And even though her father loves her, she can’t tell him how unhappy she is because her stepmother has bewitched him. One day Cinderella’s stepmother and stepsisters are invited to a ball at the royal palace. Cinderella is told she cannot go and is understandably very unhappy. However, her fairy godmother comes to the rescue and, waving her magic wand, produces some beautiful clothes for Cinderella as well as a carriage to convey her to the ball. There, she dances with the handsome prince, who falls in love with her… Just a sweet, pretty tale Not in the view of Ellen Macintosh, who has written extensively about fairy tales. "This story features the stock, two-dimensional characters of most fairy tales, and little character development is attempted," she says. Indeed, although her comment does make one wonder why simplicity of this sort should be out of place in a story for children. Be that as it may, Ellen’s main problem is with what the story implies. "Instead of standing up to her cruel stepmother and absurd stepsisters, Cinderella just waits for a fairy godmother to appear and solve her problem. But wouldn’t you want a daughter of yours to show more spirit " The story is enduring, whatever its shortcomings, and it doesn’t take much in the way of analytical skills to see its influence on a number of recent Hollywood productions, all aimed at girls aged five to fifteen. In these versions for the silver screen, the Cinderella character no longer has to clean the house and has no siblings to make her life a misery, though she persists in not showing much backbone. The character of the rich and handsome stranger, however, is retained, and in some cases really is a prince. The role of the fairy godmother is often played by coincidence or sheer luck; we live in an enlightened age when even very young children might reject the notion of fairies. The wicked stepmother may be transformed into a villain of some sort. In the majority of film versions, the heroine has a profession and is even permitted to continue working after marrying her prince — this is the twenty — first century, after all. Doesn’t the success of these films indicate that the story has relevance to children even today "Yes," admits Ellen, who sees its message as being rooted in a fundamental childhood desire for love and attention. "Most children experience a sense of inner loneliness as they are growing up and empathies with the protagonist who faces some sort of test or challenge. This can be seen in the original story of Cinderella, where the fairy godmother tells the heroine that she must learn to be gracious and confident if she is to go to the ball. She has to grow spiritually, and by maturing, she becomes attractive to the prince, thus ensuring that the ending of the story will be happy." "In the later versions, this element is missing," says Ellen, "and the theme of the story is simply that a girl’s role in life is to be more beautiful than other little girls so that she can carry off the prize: the handsome prince. Is this really what we want girls to grow up believing " |
What is Ellen’s main objection to the Cinderella story
A．(A) The heroine is treated cruelly.
B．(B) The heroine is not assertive enough.
C．(C) The ugly stepsisters are figures of ridicule.
D．(D) The stepmother is a stereotypical character.