— [http://goo.gl/hh9vhF] Nettie Stevens was one of the first female scientists to make a name for herself in the biological sciences._______________________To prove the fertilizing power of semen (which contain sperm), in 1784, scientists put pants on male frogs before allowing them to mate. It was noted that the resulting eggs never developed.

:: RT: Google Doodle celebrates on July 7, 2016 Nettie Stevens' 155th birthday ▶ https://goo.gl/gLj17w ◀ Nettie Stevens, in 1905, discovered what were later named the X and Y chromosomes. ↠ #NettieStevens #Genetics #WomenInStem #Xchromosome #SexChromosomes #SexDetermination

Nettie Stevens was the major source of evidence” for chromosomal determination of sex. "The determination of sex is not by inheritance but by the combined effect of external conditions." wrote Edmund Beecher Wilson in The Cell in Development and Inheritance (1896). A definitive statement that was expanded on later in the work to state that "...it is certain that sex as such is not inherited”. While stated with authority by a leading biologist of the time, such answers to the question of how sex is determined were not satisfying and required more explanation, forcing contemporaries to look more critically at inheritance patterns.

Nettie Stevens discovered that in some species chromosomes are different among the sexes, by observations of insect chromosomes. The discovery was the first time that observable differences of chromosomes could be linked to an observable difference in physical attributes, i.e. if an individual is a male or a female.

Nettie Stevens: A Discoverer of Sex Chromosomes.


Sex Determination: More Complicated Than You Thought ::

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"According to most biologists and historians who have written on the subject, the crucial step in the discovery of chromosomal sex determination was taken in 1905 by Nettie M. Stevens," PDF ::

Nettie Maria Stevens and the Discovery of Sex Determination by Chromosomes, PDF - Official Website - BenjaminMadeira


New uploaded videos on Youtube about #Sex Chromosomes ::

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Sources :

• [1] Boveri, Theodor. "Über mehrpolige Mitosen als Mittel zur Analyse des Zellkerns." [On Multipolar Mitosis as a Means of Analysis of the Cell Nucleus]. Physikalisch-Medizinischen Gesellschaft zu Würzburg 35 (1902): 67–90. http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/15991

• [2] Brush, Stephen G. "Nettie M. Stevens and the Discovery of Sex Determination by Chromosomes." Isis 69 (1978): 162–72.

• [3] Lenay, Charles. "Hugo De Vries: From the Theory of Intracellular Pangenesis to the Rediscovery of Mendel." Comptes Rendus de l'Académie des Sciences - Series III - Sciences de la Vie 323 (2000): 1053–60.

• [4] Maienschein, Jane. "What Determines Sex? A Study of Converging Approaches, 1880–1916." Isis 75 (1984): 457–80.

• [5] McClung, Clarence Erwin. "The Accessory Chromosome–Sex Determinant?" The Biological Bulletin 3 (1902): 43–84. http://www.biolbull.org/content/3/1-2/43.full.pdf+html

• [6] Mendel, Gregor Johann. “Versuche über Pflanzen-Hybriden” [Experiments Concerning Plant Hybrids].” Verhandlungen des naturforschenden Vereines in Brünn [Proceedings of the Natural History Society of Brünn] IV (1865): 3–47. Reprinted in Fundamenta Genetica, ed. Jaroslav Kříženecký, 15–56. Prague: Czech Academy of Sciences, 1966. http://www.mendelweb.org/Mendel.html

• [7] Ogilvie, Marilyn Bailey and Clifford J. Choquette. "Nettie Maria Stevens (1861-1912): Her Life and Contributions to Cytogenetics." Proceedings of the American Philosophical Society 125 (1981): 292–311.

• [8] Stevens, Nettie Maria. Studies in Spermatogenesis with Especial Reference to the "Accessory Chromosome." Washington D.C.: Carnegie Institution of Washington, 1905.

• [9] Stevens, Nettie Maria. Studies in Spermatogenesis with a Comparative Study of the Heterochromosomes in Certain Species of Coleoptera, Hemiptera and Lepidoptera, with Especial Reference to Sex Determination. Washington D. C.: Carnegie Institution of Washington, 1906.

• [10] Sutton, Walter S. "On the morphology of the chromosome group in Brachystola magna." The Biological Bulletin 4 (1902): 24–39. http://www.biolbull.org/content/4/1/24.full.pdf+html

• [11] Wilson, Edmund Beecher. “Studies on Chromosomes,” 1–13 in Journal of Experimental Zoology, (1905–1912). http://dx.doi.org/10.5962/bhl.title.23656

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