Studies in Spermatogenesis Part II
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Her career span was short, but she published approximately 40 papers. Her single-mindedness and devotion, combined with keen powers of observation; her thoughtfulness and patience, united to a well-balanced judgment, account, in part, for her remarkable accomplishment. Modern cytological work involves an intricacy of detail, the significance of which can be appreciated by the specialist alone; but Miss Stevens had a share in a discovery of importance, and her work will be remembered for this, when the minutiae of detailed investigations that she carried out have become incorporated in the general body of the subject.
To celebrate her th birthday, on July 7, Google created a doodle showing Stevens peering through a microscope at XY chromosomes. From Wikipedia, the free encyclopedia. Nettie Stevens.
Studies in Spermatogenesis (), by Nettie Maria Stevens | The Embryo Project Encyclopedia
Cavendish, Vermont , United States. Baltimore, Maryland , United States. Science, Vol. June Stevens and the Discovery of Sex Determination by Chromosomes". Retrieved July 7, Heilbron ed. Archived from the original on August 17, Retrieved August 18, American Association of University Women. September 13, Molecular Reproduction and Development. Archived from the original on March 14, Retrieved July 6, Magner, A History of the Life Sciences , 3rd ed. October 12, Bibcode : Sci The Mechanism of Mendelian Genetics.
New York, Henry Holt and Company. Google Docs. The Marine Biological Laboratory. Archived from the original on March 31, May 5, Retrieved August 14, Inductees to the National Women's Hall of Fame. Margaret Sanger Sojourner Truth. Carrie Chapman Catt Frances Perkins. Belva Lockwood Lucretia Mott.
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Although Stevens did not find extra chromosomes in her work with aphids in , Stevens held that the sperm and the eggs somehow determined the sex of an offspring. Studies in Spermatogenesis has two parts. Part I, published in , begins with a reference to McClung's theory of accessory chromosomes and states the need to further investigate the theory as a potential sex determination mechanism. Stevens next introduces five insects previously unstudied for sex determination : termite Zootermopsis angusticollis , sand cricket Stenopelmatus , German cockroach Blattella germanica , mealworm Tenebrio molitor , and aphid Aphis oenotherae.
Stevens describes the methods used to microscopically view the testes of each insect. Stevens details her results for the individual stages of spermatogenesis and for the presence or absence of accessory chromosomes for each insect. The results also reference figures that are present at the end of the book, providing visual representations of the results. Stevens concludes each section with a summary of the important observations made for each particular insect.
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Part I concludes with a general discussion of each insect in relation to McClung's hypothesis and reiterates the importance of the findings in Tenebrio molitor , namely that in both somatic and sex cells, one particular chromosome was smaller in male cells than the corresponding chromosome in female cells. Stevens focuses on beetles, specifically the species Tenebrio molitor. Stevens searched for similar sexual differentiation mechanisms in species similar to T. She identifies nineteen species belonging to eight different families in which sex determination is identified by a small chromosomal element similar to T.
Stevens devotes a much of Studies in Spermatogenesis to her work with the mealworm by describing both the germ cells precursor cells to egg and sperm cells and the somatic cells of mealworms.
In Vitro Spermatogenesis; Past, Present, and Future
At the time, researchers had noted that somatic cells contained a number of chromosomes, with one half contributed by each parent. They had also noted that germ cells contained half of the number chromosomes found in somatic cells. In mealworms, Stevens found ten large chromosomes in eggs and either ten large or nine large and one small chromosome in the spermatocytes, which later mature into sperm cells. Stevens also describes the somatic cells of mealworms as containing twenty large chromosomes in females, and nineteen large and one small chromosome in males.
After repeatedly observing that the comparatively small chromosomes were present only in male somatic and germ cells , Stevens concluded that an egg fertilized by a male sex cell spermatozoon that contains the small chromosome will develop into a male. Likewise, an egg fertilized by a spermatozoon containing the larger chromosome will develop into a female. However, Wilson remained skeptical about attributing sex to a particular type of chromosome until further information supported the theory.
Wilson suggested instead that the intensity of chromosomes varied between sexes and that environmental causes could affect their intensity. After Stevens published her results in September , Wilson revised his previous publications, deleting references to environmental influences. Instead, Wilson cited Stevens's work as supporting his original theories. Studies in Spermatogenesis provides one of the first observations of XY sex- determination. Stevens's findings allowed researchers to locate the material of Mendelian inheritance that passed specific traits, in this case the sex of the organism Tenebrio molitor , through a distinct chromosomal element.