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"The Adaptive Significance of Temperature-Dependent Sex Determination in a Reptile" (2008), by Daniel Warner and Richard Shine
In 2008 researchers Daniel Warner and Richard Shine tested the Charnov-Bull model by conducting experiments on the Jacky dragon (Amphibolurus muricatus), in Australia. Their results showed that temperature-dependent sex determination(TSD) evolved in this species as an adaptation to fluctuating environmental temperatures. The Charnov-Bull model, proposed by Eric Charnov and James Bull in 1977, described the evolution of TSD, although the model was, for many years, untested.
Format: Articles
Subject: Experiments
Photograph 51, by Rosalind Franklin (1952)
On 6 May 1952, at King’s College London in London, England, Rosalind Franklin photographed her fifty-first X-ray diffraction pattern of deoxyribosenucleic acid, or DNA. Photograph 51, or Photo 51, revealed information about DNA’s three-dimensional structure by displaying the way a beam of X-rays scattered off a pure fiber of DNA. Franklin took Photo 51 after scientists confirmed that DNA contained genes. Maurice Wilkins, Franklin’s colleague showed James and Francis Crick Photo 51 without Franklin’s knowledge. Watson and Crick used that image to develop their structural model of DNA.
Format: Articles
Subject: Publications
The Meselson-Stahl Experiment (1957–1958), by Matthew Meselson and Franklin Stahl
In an experiment later named for them, Matthew Stanley Meselson and Franklin William Stahl in the US demonstrated during the 1950s the semi-conservative replication of DNA, such that each daughter DNA molecule contains one new daughter subunit and one subunit conserved from the parental DNA molecule. The researchers conducted the experiment at California Institute of Technology (Caltech) in Pasadena, California, from October 1957 to January 1958.
Format: Articles
Subject: Processes, Experiments
Categorization of Conservative, Semi-Conservative, and Dispersive DNA Replication Theories (1953–1956)
In 1956, Gunther Stent, a scientist at the University of California Berkeley in Berkeley, California, coined the terms conservative, semi-conservative, and dispersive to categorize the prevailing theories about how DNA replicated. Stent presented a paper with Max Delbrück titled “On the Mechanism of DNA Replication” at the McCollum-Pratt Symposium at Johns Hopkins University in Baltimore, Maryland. In response to James Watson and Francis Crick’s proposed structure of DNA in 1953, scientists debated how DNA replicated.
Format: Articles
Subject: Theories
Franklin William Stahl (1929– )
Franklin William Stahl studied DNA replication, bacteriophages, and genetic recombination in the US during the mid-twentieth and early twenty-first centuries. With his colleague Matthew Meselson, Stahl performed an experiment called the Meselson-Stahl experiment, which provided evidence for a process called semi-conservative DNA replication. Semi-conservative replication is a process in which each strand of a parental DNA double helix serves as a template for newly replicated daughter strands, so that one parental strand is conserved in every daughter double helix.
Format: Articles
Subject: People
Social Implications of Non-Invasive Blood Tests to Determine the Sex of Fetuses
By 2011, researchers in the US had established that non-invasive blood tests can accurately determine the gender of a human fetus as early as seven weeks after fertilization. Experts predicted that this ability may encourage the use of prenatal sex screening tests by women interested to know the gender of their fetuses. As more people begin to use non-invasive blood tests that accurately determine the sex of the fetus at 7 weeks, many ethical questions pertaining to regulation, the consequences of gender-imbalanced societies, and altered meanings of the parent-child relationship.
Format: Articles
Subject: Reproduction, Ethics, Legal
Evaluation of the Newborn Infant--Second Report (1958), by Virginia Apgar et al.
Virginia Apgar and colleagues wrote “Evaluation of the Newborn Infant—Second Report” in 1958. This article explained that Apgar’s system for evaluating infants’ condition after birth accurately predicted the health of infants. Apgar had developed the scoring system in 1953 to provide a simple method for determining if an infant needed medical attention after birth.
Format: Articles
Subject: Reproduction, Publications
Title X Family Planning Program (1970–1977)
The Family Planning Services and Public Research Act of 1970, often called Title X Family Planning Program, is a US federal law that provides federal funding for family planning services to low income or uninsured families. The US federal government passed the law, Public Law 91-572, in 1970 as an amendment to the Public Health Services Act of 1944. The Act created the Office of Population Affairs (OPA) under the Secretary of Health, Education, and Welfare (here called the Secretary).
Format: Articles
Subject: Reproduction, Legal
The Debate over DNA Replication Before the Meselson-Stahl Experiment (1953–1957)
Between 1953 and 1957, before the Meselson-Stahl experiment verified semi-conservative replication of DNA, scientists debated how DNA replicated. In 1953, James Watson and Francis Crick proposed that DNA was composed of two helical strands that wound together in a coil. Their model suggested a replication mechanism, later termed semi-conservative replication, in which parental DNA strands separated and served as templates for the replication of new daughter strands.
Format: Articles
Subject: Theories
Jane Marion Oppenheimer (1911-1966)
Jane Marion Oppenheimer, embryologist and historian of science and medicine, was born on 19 September 1911 in Philadelphia, Pennsylvania, to Sylvia Stern and James H. Oppenheimer. After studying zoology at Bryn Mawr College, Oppenheimer received her AB degree in 1932. Oppenheimer received her PhD in embryology at Yale University in 1935 and worked as a research fellow from 1935-1936. While at Yale she was influenced by the work of Ross Granville Harrison and John Spangler Nicholas, the latter of whom was Oppenheimer's PhD advisor.
Format: Articles
Subject: People
Epithelium
Frederik Ruysch, working in the Netherlands, introduced the term epithelia in the third volume of his Thesaurus Anatomicus in 1703. Ruysch created the term from the Greek epi, which means on top of, and thele, which means nipple, to describe the type of tissue he found when dissecting the lip of a cadaver. In the mid nineteenth century, anatomist Albrecht von Haller adopted the word epithelium, designating Ruysch's original terminology as the plural version. In modern science, epithelium is a type of animal tissue in which cells are packed into neatly arranged sheets.
Format: Articles
"Alternative Sources of Human Pluripotent Stem Cells" (2005), by Leon Kass and the President’s Council on Bioethics
Human pluripotent stem cells are valued for their potential to form numerous specialized cells and for their longevity. In the US, where a portion of the population is opposed to destruction of human embryos to obtain stem cells, what avenues are open to scientists for obtaining pluripotent cells that do not offend the moral sensibilities of a significant number of citizens?
Format: Articles
Subject: Publications, Ethics
Julia Bell (1879-1979)
Julia Bell worked in twentieth-century Britain, discovered Fragile X Syndrome, and helped find heritable elements of other developmental and genetic disorders. Bell also wrote much of the five volume Treasury of Human Inheritance, a collection about genetics and genetic disorders. Bell researched until late in life, authoring an original research article on the effects of the rubella virus of fetal development (Congenital Rubella Syndrome) at the age of 80.
Format: Articles
Subject: People
Martius Flap Procedure to Repair Obstetric Fistulas
The Martius flap procedure is a surgical procedure used to treat obstetric fistulas in women. Heinrich Martius developed the procedure in twentieth century Germany to treat women with urinary incontinence caused by stress, and later doctors used it to repair obstetric fistulas. Fistulas occur in pregnant women when a hole is torn between the vagina and the urinary tract (called vesicovaginal) or the vagina and the rectum (called rectovaginal). The hole, or fistula, occurs in the tissue separating two organs and therefore obstetric fistulas result in either urinary or fecal incontinence.
Format: Articles
Subject: Technologies, Disorders
"The Cell-Theory" (1853), by Thomas Henry Huxley
The Cell-Theory was written by Thomas Henry Huxley in Britain and published in 1853 by The British and Foreign Medico-Chirurgical Review. The twenty-two page article reviews twelve works on cell theory, including those in Germany by Caspar Friedrich Wolff in the eighteenth century and by Karl Ernst von Baer in the nineteenth century. Huxley spends much of The Cell-Theory on a cell theory proposed in the late 1830s by Matthias Schleiden and Theodor Schwann in Germany.
Format: Articles
Subject: Publications
Ignaz Philipp Semmelweis (1818-1865)
Ignaz Philipp Semmelweis demonstrated that the use of disinfectants could reduce the occurrence of puerperal fever in patients in nineteenth century Austria. Puerperal fever is a bacterial infection that can occur in the uterine tract of women after giving birth or undergoing an abortion. Semmelweis determined that puerperal fever is contagious and argued that the unhygienic practices of physicians, like examining patients after performing autopsies, caused the spread of puerperal fever.
Format: Articles
Subject: People
Dinosaur Egg Parataxonomy
Dinosaur egg parataxonomy is a classification system that organizes dinosaur eggs by descriptive features such as shape, size, and shell thickness. Though egg parataxonomy originated in the nineteenth century, Zi-Kui Zhao from Beijing, China, developed a modern parataxonomic system in the late twentieth century. Zhao's system, published in 1975, enabled scientists to organize egg specimens according to observable features, and to communicate their findings.
Format: Articles
Subject: Theories
The Hedgehog Signaling Pathway in Vertebrates
The hedgehog signaling pathway is a mechanism that regulates cell growth and differentiation during embryonic development, called embryogenesis, in animals. The hedgehog signaling pathway works both between cells and within individual cells.
Format: Articles
Subject: Theories
President George W. Bush's Announcement on Stem Cells, 9 August 2001
On 9 August 2001, US President George W. Bush gave an eleven-minute speech from his ranch in Crawford, Texas, on the ethics and fate of federal funding for stem cell research. Bush also announced the creation of a special council to oversee stem cell research. In the speech President Bush acknowledged the importance of issues surrounding stem cell research to many Americans, presented different arguments in favor of and opposing embryonic stem cell research, and explained his decision to limit but not completely eliminate potential federal funding for embryonic stem cell (ESC) research.
Format: Articles
Subject: Legal
"Generation of Induced Pluripotent Stem Cells Using Recombinant Proteins" (2009), by Hongyan Zhou et al.
Induced pluripotent stem cells (iPSCs) are studied carefully by scientists not just because they are a potential source of stem cells that circumvents ethical controversy involved with experimentation on human embryos, but also because of their unique potential to advance the field of regenerative medicine. First generated in a lab by Kazutoshi Takahashi and Shinya Yamanaka in 2006, iPSCs have the ability to differentiate into cells of all types.
Format: Articles
Subject: Publications
Georgeanna Seegar Jones (1912-2005)
Georgeanna Seegar Jones was a reproductive endocrinologist who created one of America' s most successful infertility clinics in West Virginia and eventually, along with her husband Howard W. Jones MD, performed the first in vitro fertilization in America, leading to the birth of Elizabeth Jordan Carr. Jones was born in Baltimore, Maryland, on 6 July 1912. Her father, Dr. John King Beck Emory Seegar, was a practicing physician at the time working in the field of obstetrics.
Format: Articles
Subject: People, Reproduction
Andrew Francis Dixon (1868-1936)
Andrew Francis Dixon studied human anatomy and egg cells at the turn of the twentieth century in Ireland and Great Britain. Dixon studied the sensory and motor nervous system of the face, the cancellous bone tissue of the femur, supernumerary kidneys, and the urogenital system. In 1927 Dixon described a mature human ovarian follicle. This follicle, Dixon noted, contained an immature human egg cell (oocyte) with a visible first polar body and the beginnings of the second polar body.
Format: Articles
Subject: People
Ectoderm
Ectoderm is one of three germ layers--groups of cells that coalesce early during the embryonic life of all animals except maybe sponges, and from which organs and tissues form. As an embryo develops, a single fertilized cell progresses through multiple rounds of cell division. Eventually, the clump of cells goes through a stage called gastrulation, during which the embryo reorganizes itself into the three germ layers: endoderm, ectoderm, and mesoderm. After gastrulation, the embryo goes through a process called neurulation, which starts the development of nervous system.
Format: Articles
Subject: Processes
Max Ludwig Henning Delbruck (1906–1981)
Max Ludwig Henning Delbrick applied his knowledge of theoretical physics to biological systems such as bacterial viruses called bacteriophages, or phages, and gene replication during the twentieth century in Germany and the US. Delbrück demonstrated that bacteria undergo random genetic mutations to resist phage infections. Those findings linked bacterial genetics to the genetics of higher organisms. In the mid-twentieth century, Delbrück helped start the Phage Group and Phage Course in the US, which further organized phage research.
Format: Articles
Subject: People
John Chassar Moir (1900–1977)
John Chassar Moir lived in Scotland during the twentieth century and helped develop techniques to improve the health of pregnant women. Moir helped to discover compounds that doctors could administer to women after childbirth to prevent life-threatening blood loss. Those compounds included the ergot alkaloid called ergometrine, also called ergonovine, and d-lysergic acid beta-propanolamide. Moir tested ergometrine in postpartum patients and documented that it helped prevent or manage postpartum hemorrhage in women.
Format: Articles
Subject: People, Reproduction, Disorders