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摩尔根的诺贝尔奖和一段故事 精选

已有 10549 次阅读 2012-1-29 10:08 |个人分类:科学那些事儿|系统分类:科普集锦|关键词:摩尔根,诺贝尔奖,果蝇,蚜虫| 诺贝尔奖, 蚜虫, 摩尔根, 果蝇

The Nobel Prize in Physiology or Medicine 1933 was awarded to Thomas H. Morgan "for his discoveries concerning the role played by the chromosome in heredity".

托马斯-亨特-摩尔根(Thoman Hunt Morgan),现代遗传学的奠基人,由于其染色体遗传理论方面的开创性工作而获得1933年诺贝尔生理学或医学奖。

摩尔根对于学生物的人来说肯定很有名,对于没学生物的人来说也很有名。一方面他常被作为科学史上的一个重要人物介绍,另一方面还常被很多给小孩子读的励志图书介绍。

摩尔根的染色体理论和基因连锁交换定律主要是基于对昆虫尤其是果蝇的研究。在遗传学课本中(起码我学过的课本中),提到的只有摩尔根果蝇的工作。但实际上,在果蝇性别决定工作之前,摩尔根(及其他研究者)已经研究了蚜虫的性别决定。对于蚜虫类的研究也为摩尔根最终接受性别决定的染色体理论提供了重要证据。

大约从1906年开始,摩尔根就开始研究根瘤蚜(phylloxerans)和其他蚜虫类(aphids)的性别决定,关注的主要问题是染色体和性别决定之间的关系。广义上根瘤蚜也属于蚜虫类,蚜科(狭义上的蚜虫类)、球蚜科和根瘤蚜科共同组成了蚜虫类。蚜虫类很大的特点是其生活周期为有性生殖和孤雌生殖交替。根瘤蚜为卵生,生活周期中有一段时间为孤雌卵生,有性生殖时则由孤雌卵孵化为雄性和雌性,交配后产卵完成有性生殖。蚜科为卵胎生,大部分时间为孤雌胎生,有性生殖时由孤雌蚜直接产生雄性蚜和雌性蚜,交配产卵。由于根瘤蚜的雄性和雌性都来自于未受精的孤雌卵,所以摩尔根想看看是什么决定了有些卵(一般是比较小的卵)发育成雄性而有些卵(一般是比较大的卵)发育成雌性。

1906年,摩尔根报道了对几种根瘤蚜染色体的研究。他发现雄性卵和雌性卵在发育过程中染色体数目没有任何差别。于是他观察了两类卵的细胞质,发现一个唯一的区别:雄性卵有比较少的卵黄,并且卵中心有一团明显的细胞质聚集物;而雌性卵则卵黄较多,且没有那团物质。雄性卵中那团细胞质应该形成了雄性的睾丸。基于这些结果,摩尔根认为是细胞质因素决定了根瘤蚜的性别。

实际上在1905年, Nettie StevensEdmund Wilson已经给出了染色体决定性别的明显证据(见下面几段引文及参考文献)。一开始的时候摩尔根对染色体决定论持怀疑态度,他认为细胞质和生理因素在性别决定上起了更重要的作用,也因此他会在早期有关蚜虫的论文中给出细胞质方面的解释。现在很多人认识到,实际上StevensWilson才是最早提出染色体性别决定的人(当然这也并没有削弱摩尔根工作的重要性,见下面引文Wilson对摩尔根工作的评价)。

1909年,比他在Science发表关于果蝇性别决定的论文早一年,摩尔根在Science发表了关于根瘤蚜和蚜虫类(狭义)性别决定的论文,比1906年的论文相比有了更细致的观察。虽然他发现在雄性中发生了染色体减少的现象,并且称“与性别决定有关的明显的染色体变化”,但他依然认为孤雌卵的性别(雄性卵或雌性卵)在卵发育过程中染色体数目发生变化之前已经决定了。实际上,这篇论文中摩尔根依然持有细胞质决定的观点。并且虽然题目是根瘤蚜和蚜虫类的性别决定,他主要还是基于对根瘤蚜的讨论,只是在一处地方提及了在蚜虫类(狭义)中也有类似的发现(其他蚜虫类的工作主要是Stevens在那几年所发表)。

19105月,摩尔根实验室发现了一只白眼雄性果蝇,这只白眼果蝇意义重大,它可以让摩尔根进行很多的杂交试验,从而提供一个性状性别决定的经典例子。19107月,摩尔根在Science发表了他一系列的杂交工作的发现。这篇文章暗示果蝇眼睛颜色的控制基因存在于X染色体上。实际上在这篇Science论文中,摩尔根并没有明确的这样表述。这跟他一开始认为细胞质和生理因素在性别决定上起更重要的作用有关。后来更多的果蝇性别相关性状的研究使得摩尔根开始接受性别决定的染色体理论,以及染色体是孟德尔遗传的物理载体。1912年,摩尔根明确的将根瘤蚜性别发育与其性染色体差异联系起来。

1933年诺贝尔奖颁奖典礼上,介绍人提到摩尔根成功的三个关键因素。1)方法的使用:经典的统计遗传学加上微观遗传学方法;2)选对了实验材料:果蝇实在是很好的模式动物,所以摩尔根能够比同行更早的获得更多新的发现;3)(很少有人像摩尔根一样能够)团结那么多好学生和合作者。其实这几个关键因素,不管在哪个年代,都是非常重要的。很遗憾,介绍人并没有提到蚜虫,实际上从上面介绍可以发现,基于蚜虫的研究对于摩尔根理论的发展有非常重要的贡献。

1933年诺贝尔奖颁奖典礼上,介绍人还提到:孟德尔1866年发表了介绍豌豆杂交的经典论文Versuche über Pflanzen-HybridenExperiments on Plant Hybridization),而摩尔根于1866年出生。多么有意思的巧合!

据说19105月那只有名的白眼雄性果蝇问世的时候,摩尔根家刚有了第三个孩子,当他去医院看望妻子的时候,妻子问他“那只白眼果蝇怎么样了?”看来,贤内助的关心一直是研究成功的关键。

 

有关StevensWilson的发现:

In 1905, Wilson published two papers on the idiochromosomes (accessory chromosomes) of the true bugs. Here, he confirmed McClung's view that the accessory chromosomes, at least in some cases, were correlated with sex, and he corrected McClung's notion that the accessory chromosome was the male determinant. The female, he said, had the extra chromosome. This assertion was based on his observation of chromosome morphology in the bug Anasa and on the theory that, in some bugs, there existed in the male both large and small idiochromosomes (later to be termed by Wilson X and Y, respectively). The smaller one, he argued, which was always found in the male, could be absent altogether in some species. From the sperm of the males, then, half would receive the large idiochromosome and half would receive either the small idiochromosome or no sex chromosome at all, depending on the species.

In same year, Nettie M. Stevens of Bryn Mawr published her work on sex determination in insects. Her first paper, published in the same volume of the Journal of Experimental Zoology as Wilson's, claimed that in two species of aphids, no accessory chromosome could be seen during spermatogenesis. However, by observing spermatogenesis in an organism with only five, clearly distinct, chromosomes, she confirmed Sutton and Boveri's theory that the homologues each went to separate cells during meiosis. By September 1905, the Carnegie Institution of Washington began publishing her complete study of the mode of sex determination in over fifty species of insects and one primitive chordate. Most important of these studies were her observations on the mealworm beetle, Tenebrio molliter. Here, somatic cells in the females had twenty large chromosomes, while those of the male had nineteen large chromosomes, plus one small one. The unfertilized eggs had ten large chromosomes, whereas the sperm had either ten large chromosomes or nine large and one small chromosome. She, too, corrected the details in McClung's theory. By September 1906, Stevens had discovered the mode of sex determination for over 42 species of beetles. Of these species, 85.7 percent had their sex determined by the method of unequal partners (what we now call X and Y chromosomes), whereas 14.3 percent had it determined by the single accessory chromosome method (XO type determination).

Wilson attempted to relate sex determination to physiological differences arising from different chromosome constitutions. He believed that the chromosomes determined the sex of the individual, and that the smaller chromosome of the male represented a degenerate female chromosome. The sex characteristics, he held, would arise from differences in the degree or intensity of chromosomal activity rather than from qualitative differences between the two chromosomes.

Stevens, however, believed that it was more probable that qualitative differences existed between the large and small asymmetrically paired chromosomes, and that these were the differences that determined sex. More important, though, was her belief that a dominance-recessive Mendelian inheritance of sex was possible through selective fertilization.

The chromosomal determination of sex, for which Wilson was the major spokesman and Nettie Stevens the major source of evidence, could not be completely substantiated without an explanation of how it was accomplished in the parthenogenetically reproducing species. It was what Wilson called "the brilliant discoveries of Morgan and von Baehr" that showed that sex was determined by chromosomes in these species; but as we shall see, even as late as 1910, Morgan refused to believe in what he called the "McClung-Stevens-Wilson hypothesis."

以上原文引自:Gilbert S.F. 2010. The Embryological Origins of the Gene Theory. In: Gilbert S.F. 2010. Developmental Biology, Ninth Edition. Sinauer Associates, Inc. (PDF link)

 

相关文献:

Stevens NM. 1905. Studies in spermatogenesis with especial reference to the "accessory chromosome" (Washington, D.C.; Carnegie Institution). (A study of Stevens's work according it priority over Wilson's has been prepared by Dr. Stephen G. Brush and will appear in Isis. He notes that Morgan, while disagreeing with her theory, gave Stevens unqualified support in his recommendation letter to the Carnegie Institution.)

Stevens NM. 1905. A study of the germ cells of Aphis rosae and Aphis oenotherae. Journal of Experimental Zoology 2: 313-333. (This paper was awarded the prize of one thousand dollars offered in 1904 by the “Association for Maintaining the American Woman's Table at the Zoölogical Station at Naples, and for Promoting Scientific Research among Women)

Wilson EB. 1905. Studies on chromosomes. I. The behavior of the idiochromosomes in hemiptera. Journal of Experimental Zoology 2: 371-405.

Wilson EB. 1905. The chromosomes in relation to the determination of sex in insects. Science 22: 501-502. (It is more probable, for reasons that will be set forth hereafter, that the difference between eggs and spermatozoa is primarily due to differences of degree or intensity, rather than of kind, in the activity of the chromosome groups in the two sexes.)

Stevens NM. 1906. Studies on the germ cells of aphids. Carnegie Institution of Washington, Publication No. 51. (感兴趣可以向我索要PDF)

Morgan TH. 1906. The male and female eggs of phylloxerans of the hickories. Biological Bulletin 10: 201-206.

Stevens NM. 1909. An unpaired heterochromosome in the aphids. Journal of Experimental Zoology 6: 115-123.

Morgan TH. 1909. Sex determination and parthenogenesis in phylloxerans and aphids. Science 29: 234-237.

Morgan TH. 1909. A biological and cytological study of sex determination in phylloxerans and aphids. Journal of Experimental Zoology 7: 239-351.

Morgan TH. 1910. Sex limited inheritance in Drosophila. Science 32: 120-122.

Morgan TH. 1911. An attempt to analyze the constitution of the chromosomes on the basis of sex-limited inheritance in Drosophila. Journal of Experimental Zoology 11: 365-413.

Morgan, T. H., 1912. An attempt to analyze the constitution of the chromosomes on the basis of sex-limited inheritance in Drosophila. Journal of Experimental Zoology 11: 365-413.

Morgan, T. H., 1912. The elimination of the sex chromosomes from the male-producing eggs of phylloxerans. Journal of Experimental Zoology 12: 479-498.

Morgan, T. H., 1915. The predetermination of sex in phylloxerans and aphids. Journal of Experimental Zoology 19: 285-321.

Morgan TH, Sturtevant AH, Muller HJ, Bridges CB. 1915. The Mechanism of Mendelian heredity. Henry Holt and Company. (PDF link)

Morgan, T. H. 1928 (Revised and Enlarged Edition). The Theory of the Gene. Yale University Press. (PDF link)

Kenney DE, Borisy GG. 2009. Thomas Hunt Morgan at the Marine Biological Laboratory: Naturalist and Experimentalist. Genetics 181:  841-846. (值得一读!Full text link)


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