Researchers have created male mice with no trace of a Y chromosome, supposedly the defining hallmark of being male.
Reproductive biologist Monika Ward of University of Hawaii in Honolulu and colleagues started with mice that have only one X chromosome (and no second sex chromosome). Normally those animals would develop as females. But when the researchers manipulated genes found on the X and another chromosome, the mice became males that could produce immature sperm. Those engineered males fathered offspring with reproductive assistance from the researchers, who injected the immature sperm into eggs, Ward and colleagues report in the Jan. 29 Science.
The experiments demonstrate that there are multiple ways to make males, says Richard Behringer, a developmental geneticist at MD Anderson Cancer Center in Houston. “They’ve done it without any Y chromosome gene information,” he says “There’s not even a sniff of the Y around.”
At first glance, the experiments would seem to suggest Y chromosomes aren’t necessary for reproduction, which hints that evolution may eventually show Y’s the door. “To me it is a paradigm of the decline and fall of the Y chromosome,” says reproductive biologist Jennifer Marshall Graves of La Trobe University in Melbourne, Australia.
But Ward and other researchers say the Y isn’t going anywhere and that interpreting the new results as the chromosome’s death knell is wrong. Because the Y-less males needed help to reproduce, “clearly we need the Y chromosome for full natural male reproduction,” says Mary Ann Handel, a reproductive biologist at the Jackson Laboratory in Bar Harbor, Maine.
Ward and colleagues had previously shown that two Y chromosome genes—Sry and Eif2s3y—are crucial for male mouse development. Sry is a master gene that turns on male developmental programming in early embryos. It turns on a gene called Sox9, which then sets off a biochemical chain reaction that leads to male development.
But in the new experiments, the researchers turned on Sox9 through other means. Activating Sox9 in a genetically female embryo will cause it to develop as a male, Ward and colleagues found. But those males didn’t make sperm. “The testes were empty,” says Ward.
In order to produce sperm, mice need the Eif2s3y gene, the researchers had previously discovered. In the new experiment, the mice were missing the gene because they didn’t have Y chromosomes. So researchers substituted a similar gene from the X chromosome called Eif2s3x. Only one copy of the Y version is needed to make immature, tailless sperm, but it takes at least five copies of the X version to do the same thing. “This indicates that the Y chromosome gene is the strong one,” says Ward.
Her research suggests that the Y chromosome has optimized production from genes that are necessary for making males. Making just the right dose of male development factors is how the Y protects itself from evolutionary erasure, Ward says. “Our work does not support that the Y chromosome will disappear.”
Graves disagrees, Ward’s work is “a lovely example of how you can lose even a really important gene,” she says. At least two species of rodents have already jettisoned their Y chromosomes entirely. Primates, including humans, don’t have Eif2s3y genes on their Y chromosomes. The new work may help explain how primates get along without the gene, Graves suggests, and the research may “give us useful information about what happens at the end of the Y chromosome.”
1.Which of the following is CORRECT according to the passage?
2.Why is Eif2s3Y gene crucial for male mouse development?
3.Which of the following is INCORRECT according to the passage?
4.What can be the best title for this passage?
问题1选项
A.Mice with only one X chromosome would develop as females normally.
B.Y chromosome is definitely the hallmark of being male.
C.Those engineered male mice cannot father offspring even with reproductive assistance
D.There is only one way to make male mice from relevant experiments in the University of Hawaii.
问题2选项
A.It is a master gene that turns on male developmental programming early embryos.
B.It sets off a biochemical chain reaction that leads to male development.
C.Mice need it to produce sperm.
D.Mice need it to develop testes.
问题3选项
A.At least two species of rodents have jettisoned their Y chromosomes completely.
B.Eif2s3X, a gene from the Y chromosome, is similar with Eif2s3y.
C.Y chromosome has optimized production from gene necessary for making males.
D.Humans don't have EiSs3y genes on their Y chromosomes.
问题4选项
A.Mice Can Be Male Without Y Chromosome.
B.The Artificial Reproduction of Mice.
C.The Mysterious Y Chromosome in Mice.
D.The Male and Female Mice.
第1题:
【选项释义】
Which of the following is CORRECT according to the passage? 根据文章,下列哪个选项是正确的?
A. Mice with only one X chromosome would develop as females normally. A. 正常情况下,只有一个X染色体的老鼠会发育成雌性老鼠。
B. Y chromosome is definitely the hallmark of being male. B. Y染色体绝对是男性的标志。
C. Those engineered male mice cannot father offspring even with reproductive assistance. C. 即使有生殖辅助,这些转基因雄性老鼠也不能生育后代。
D. There is only one way to make male mice from relevant experiments in the University of Hawaii. D. 从夏威夷大学的相关实验中,只有一种方法可以制造出雄性老鼠。
【答案】A
【考查点】事实细节题。
【解题思路】根据第二段前两句“檀香山夏威夷大学的生殖生物学家Monika Ward和他的同事从只有一个X染色体的老鼠开始研究。正常情况下,这些动物会发育成雌性(Normally those animals would develop as females.)。”,理解可知,只有一个X染色体的老鼠在正常情况下,会发育成雌性老鼠,A选项正确。
【干扰项排除】
B选项“Y染色体绝对是男性的标志”,第一段“研究人员已经创造出了没有Y染色体痕迹的雄性老鼠(created male mice with no trace of a Y chromosome),Y染色体被认为是雄性的标志”可知没有Y染色体也能创造出雄性,且文中就研究者们对于Y染色体是否是雄性的典型特点这一问题发表了不同的观点,选项B中的definitely过于绝对,曲解原文;
C选项“即使有生殖辅助,这些转基因雄性老鼠也不能生育后代”根据第二段倒数第二句“在研究人员的生殖协助下,这些转基因雄鼠繁衍出了后代”可知,该项与原文相悖,反向干扰;
D选项“从夏威夷大学的相关实验中,只有一种方法可以制造出雄性老鼠”,第二段提及夏威夷大学的科学家们已经培育出没有Y染色体的雄性小鼠,所以,培育雄性小鼠的方法不是只有一个,该项曲解原文。
第2题:
【选项释义】
Why is Eif2s3Y gene crucial for male mouse development? 为什么Eif2s3Y基因对雄性小鼠的发育至关重要?
A. It is a master gene that turns on male developmental programming early embryos. A. 它是开启男性发育早期胚胎的主控基因。
B. It sets off a biochemical chain reaction that leads to male development. B. 它引发了一个生化连锁反应,导致了男性的发育。
C. Mice need it to produce sperm. C. 老鼠需要它来产生精子。
D. Mice need it to develop testes. D. 老鼠需要它来发育睾丸。
【答案】C
【考查点】事实细节题。
【解题思路】根据第八段的第一句“研究人员此前发现,为了产生精子,老鼠需要Eif2s3y基因”,理解可知,Eif2s3Y基因对雄性小鼠的发育至关重要的原因是,它能帮助老鼠产生精子,选项C符合原文。
【干扰项排除】
A选项“它是开启男性发育早期胚胎的主控基因”和B选项“它引发了一个生化连锁反应,导致了男性的发育”根据第六段最后两句“Sry是在早期胚胎中开启男性发育程序的主控基因。它启动了一种叫作Sox9的基因,然后引发了一个导致男性发育的生化连锁反应。”,理解可知,开启男性发育早期胚胎的主控基因和引发生化连锁反应的基因是Sry,而不是Eif2s3Y,属于张冠李戴;
D选项“老鼠需要它来发育睾丸”没有提到,无中生有。
第3题:
【选项释义】
Which of the following is INCORRECT according to the passage? 根据文章,下列哪个选项是错误的?
A. At least two species of rodents have jettisoned their Y chromosomes completely. A. 至少有两种啮齿动物已经完全抛弃了它们的Y染色体。
B. Eif2s3X, a gene from the Y chromosome, is similar with Eif2s3y. B. Eif2s3X是来自Y染色体的基因,与Eif2s3y相似。
C. Y chromosome has optimized production from gene necessary for making males. C. Y染色体已经优化了产生雄性所需的基因。
D. Humans don’t have Eif2s3y genes on their Y chromosomes. D. 人类的Y染色体上没有Eif2s3y基因。
【答案】B
【考查点】事实细节题。
【解题思路】根据第八段的第二和第三句“在新的实验中,老鼠缺少这种基因,因为它们没有Y染色体。因此,研究人员从X染色体上替换了一个类似的基因,叫作Eif2s3x。”,从中可知Eif2s3x来自于X染色体,而不是Y染色体,所以选项B“Eif2s3X是来自Y染色体的基因,与Eif2s3y相似”与原文相悖,但符合题意。故该题选择B项正确。
【干扰项排除】
A选项“至少有两种啮齿动物已经完全抛弃了它们的Y染色体”根据最后一段的第二句“至少有两种啮齿动物已经完全抛弃了它们的Y染色体。”可知该项符合原文,属于反向干扰;
C选项“Y染色体已经从制造雄性所需的基因中优化了生产”根据第九段的第一句“她的研究表明,Y染色体优化了产生雄性所需的基因。”可知该项符合原文,属于反向干扰;
D选项“人类的Y染色体上没有Eif2s3y基因”根据最后一段的第三句“灵长类动物,包括人类,在Y染色体上没有Eif2s3y基因”可知该项符合原文,属于反向干扰。
第4题:
【选项释义】
What can be the best title for this passage? 这篇文章的最佳标题是什么?
A. Mice Can Be Male Without Y Chromosome. A. 没有Y染色体的老鼠也可以是雄性。
B. The Artificial Reproduction of Mice. B. 老鼠的人工繁殖。
C. The Mysterious Y Chromosome in Mice. C. 老鼠的神秘Y染色体。
D. The Male and Female Mice. D. 雄性和雌性老鼠。
【答案】A
【考查点】主旨大意题。
【解题思路】文章首段提到“研究人员培育出了没有Y染色体的雄性老鼠,而Y染色体被认为是男性的标志”可知,研究者已经培育出了没有Y染色体的雄性小鼠。在之后的段落里,列举实验说明这一科学发现,由此可知,文章主要是描述关于没有Y染色体的雄性小鼠的实验。A选项“没有Y染色体的老鼠也可以是雄性”符合题意。
【干扰项排除】
B选项“鼠的人工繁殖”和C选项“老鼠的神秘Y染色体”只是部分提及,属于以偏概全;
D选项“雄性和雌性老鼠”表达太泛,不够精准,属于曲解原文。
【文章来源】Science News网站 2016
【参考译文】
研究人员培育出了没有Y染色体痕迹的雄性老鼠,Y染色体被认为是雄性的决定性标志。
檀香山夏威夷大学的生殖生物学家莫妮卡•沃德及其同事们从只有一条X染色体(没有第二性染色体)的老鼠开始研究。正常情况下,这些动物会像雌性一样发育。但当研究人员操纵X染色体和另一条染色体上的基因时,老鼠变成了能够产生未成熟精子的雄性。沃德及其同事在1月29日的《科学》杂志上报道说,研究人员将未成熟的精子注射到卵子中,在他们的生殖协助下,这些经过改造的雄性老鼠产下了后代。
休斯顿MD安德森癌症中心的发育遗传学家理查德•贝林格说,这些实验证明有多种方法产生雄性。“他们在没有任何Y染色体基因信息的情况下做到了这一点,”他说,“周围甚至连Y染色体的气味都没有。”
乍一看,这些实验似乎表明Y染色体对繁殖来说不是必要的,这暗示着进化可能最终会向Y染色体敞开大门。“在我看来,这是Y染色体衰落的一个范例,”澳大利亚墨尔本拉特伯大学的生殖生物学家詹妮弗•马歇尔•格雷夫斯说。
但沃德和其他研究人员表示,Y染色体不会消失,将新结果解释为染色体的死亡丧钟是错误的。因为没有Y染色体的雄性需要帮助来繁殖,“很明显,我们需要Y染色体来进行完全自然的雄性繁殖,”缅因州巴尔港杰克逊实验室的生殖生物学家玛丽•安•汉德尔说。
沃德及其同事们之前已经证明了两个Y染色体基因——Sry和Eif2s3y——对雄性小鼠的发育至关重要。Sry是在早期胚胎中启动雄性发育程序的主基因。它会启动一种名为Sox9的基因,然后引发一种生化连锁反应,导致雄性的发育。
但在新的实验中,研究人员通过其他方式启动了Sox9。沃德及其同事们发现,在一个基因为雌性的胚胎中激活Sox9基因会使其发育成雄性胚胎。但这些雄性并不产生精子。“睾丸是空的,”沃德说。
研究人员此前发现,为了产生精子,老鼠需要Eif2s3y基因。在新的实验中,老鼠没有这种基因,因为它们没有Y染色体。因此,研究人员从X染色体上替换了一个类似的基因,称为Eif2s3x。只需要一个Y染色体的拷贝就能制造出不成熟的无尾精子,但要做到这一点,至少需要5个X染色体的拷贝。沃德说:“这表明Y染色体基因是强基因。”
她的研究表明,Y染色体优化了产生雄性所需基因的产量。沃德说,制造合适剂量的男性发育因子是Y染色体保护自身免受进化抹杀的方式。“我们的研究并不支持Y染色体会消失的说法。”
格雷夫斯不同意这一观点,她说,沃德的工作是“一个可爱的例子,说明你甚至可以失去一个非常重要的基因。”至少有两种啮齿动物已经完全抛弃了它们的Y染色体。包括人类在内的灵长类动物的Y染色体上没有Eif2s3y基因。格雷夫斯表示,这项新工作可能有助于解释灵长类动物在没有这种基因的情况下是如何生存的,这项研究可能“为我们提供关于Y染色体末端发生的情况的有用信息”。