Embryo Project Encyclopedia Articles

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. In 1962, after Franklin’s death, Watson, Crick, and Wilkins shared the Nobel Prize in Physiology or Medicine for their findings about DNA. Franklin’s Photo 51 helped scientists learn more about the three-dimensional structure of DNA and enabled scientists to understand DNA’s role in heredity.

In April 1953, Rosalind Franklin and Raymond Gosling, published “Molecular Configuration in Sodium Thymonucleate,” in the scientific journal Nature. The article contained Franklin and Gosling’s analysis of their X-ray diffraction pattern of thymonucleate or deoxyribonucleic acid, known as DNA. In the early 1950s, scientists confirmed that genes, the heritable factors that control how organisms develop, contained DNA. However, at the time scientists had not determined how DNA functioned or its three-dimensional structure. In their 1953 paper, Franklin and Gosling interpret X-ray diffraction patterns of DNA fibers that they collected, which show the scattering of X-rays from the fibers. The patterns provided information about the three-dimensional structure of the molecule. “Molecular Configuration in Sodium Thymonucleate” shows the progress Franklin and Gosling made toward understanding the three-dimensional structure of DNA.

Sir John Bertrand Gurdon further developed nuclear transplantation, the technique used to clone organisms and to create stem cells, while working in Britain in the second half of the twentieth century. Gurdon's research built on the work of Thomas King and Robert Briggs in the United States, who in 1952 published findings that indicated that scientists could take a nucleus from an early embryonic cell and successfully transfer it into an unfertilized and enucleated egg cell. Briggs and King also concluded that a nucleus taken from an adult cell and similarly inserted into an unfertilized enucleated egg cell could not produce normal development. In 1962, however, Gurdon published results that indicated otherwise. While Briggs and King worked with Rana pipiens frogs, Gurdon used the faster-growing species Xenopus laevis to show that nuclei from specialized cells still held the potential to be any cell despite its specialization. In 2012, the Nobel Prize Committee awarded Gurdon and Shinya Yamanaka its prize in physiology and medicine for for their work on cloning and pluripotent stem cells.

Roy Chapman Andrews traveled the world studying fossils, from mammals to dinosaurs, during the first half of the twentieth century. Andrews worked and collected fossil specimens for the American Museum of Natural History (AMNH) in New York City, New York. Throughout his career, Andrews collected bones of many animal species, including a previously unknown species of a horned, herbivorous dinosaur, later named Proceratops andrewsi in his honor. Andrews published widely read narratives about his travels and field experiences, such as On the Trail of Ancient Man and Across Mongolian Plains. Andrews led expeditions for the Central Asiatic Expeditions in the Gobi Desert, which recovered many previously unknown fossil specimens. His Central Asiatic team discovered the first scientifically recognized dinosaur eggs, which provided scientists with information about the eggs that dinosaurs produced.

Oviraptor philoceratops was a small bird-like dinosaur that lived about seventy-five million years ago, during the late Cretaceous period. In 1923, George Olsen of the American Museum of Natural History (AMNH) in New York City, New York, discovered the first Oviraptor fossilized skeleton on top of a dinosaur egg nest in the Gobi Desert, Mongolia. Because of the close proximity of dinosaur and nest, when Henry Fairfield Osborn president of the AMNH published on the discovery, he assumed that the Oviraptor had died attempting to steal the eggs. However, since the initial discovery, more Oviraptor adults, eggs, and a well-preserved embryo fossil have confirmed that Oviraptors were parents who sat on their nests, a behavior called brooding common among birds. The fossils of Oviraptor philoceratops, from eggs and embryos to adults, provide evidence about dinosaur growth, development, and reproductive behaviors.

Aristotle studied developing organisms, among other things, in ancient Greece, and his writings shaped Western philosophy and natural science for greater than two thousand years. He spent much of his life in Greece and studied with Plato at Plato's Academy in Athens, where he later established his own school called the Lyceum. Aristotle wrote greater than 150 treatises on subjects ranging from aesthetics, politics, ethics, and natural philosophy, which include physics and biology. Less than fifty of Aristotle's treatises persisted into the twenty-first century. In natural philosophy, later called natural science, Aristotle established methods for investigation and reasoning and provided a theory on how embryos generate and develop. He originated the theory that an organism develops gradually from undifferentiated material, later called epigenesis.

Lynn Petra Alexander Sagan Margulis was an American biologist, whose work in the mid-twentieth century focused on cells living together in a mutually advantageous relationship, studied cells and mitochondria in the US during the second half of the twentieth century. She developed a theory for the origin of eukaryotic cells, that proposed two kinds of structures found in eukaryotic cells mitochondria in animals, and plastids in plantsÑwere once free-living bacteria that lived harmoniously and in close proximity to larger cells, a scenario called symbiosis. Margulis proposed that the larger cells eventually engulfed the free-living bacteria, resulting in cells living inside other cells, a situation called endosymbiosis. Margulis'theory became called the serial endosymbiosis theory (SET). Her work contributed to explanations of the evolution and development of life, as eukaryotic cells comprise most multicellular organisms, including their embryos.

In the 1990s, Ian Wilmut, Jim McWhir, and Keith Campbell performed experiments while working at the Roslin Institute in Roslin, Scotland. Wilmut, McWhir, and Campbell collaborated with Angelica Schnieke and Alex J. Kind at PPL Therapeutics in Roslin, a company researching cloning and genetic manipulation for livestock. Their experiments resulted in several sheep being born in July 1996, one of which was a sheep named Dolly born 5 July 1996. Dolly was the first sheep cloned and developed from the nuclei of fully differentiated adult cells, rather than from the nuclei of early embryonic cells. They published their results in Viable Offspring Derived from Fetal and Adult Mammalian Cells (abbreviated Viable Offspring) on 27 February 1997.

In 1994, Edward M. Connor and colleagues published “Reduction of Maternal-Infant Transmission of Human Immunodeficiency Virus Type 1 with Zidovudine Treatment.” Their study summarized how to reduce the transfer of human immunodeficiency virus, or HIV, from pregnant women to their fetuses with Zidovudine, otherwise known as AZT. HIV is a virus that weakens the immune system by destroying white blood cells, a part of the body’s immune system. Fifteen to forty percent of infants born to HIV-positive mothers become infected during fetal development, labor and delivery, or breast-feeding. From April 1991 to December 1993, Connor and his colleagues researched HIV-positive pregnant women who took AZT, a drug that treats but does not cure an HIV infection. In their article, Conner and colleagues showed that AZT decreased the maternal-infant transmission of HIV and helped decrease infant mortality due to the viral infection.