Embryo Project Encyclopedia

Between 1934 and 1945, George Beadle developed a hypothesis that each gene within the chromosomes of organisms each produced one enzyme. Enzymes are types of proteins that can catalyze reactions inside cells, and the figure shows that each enzyme controls a stage in a series of biochemical reactions. The top box in this figure represents a normal process of enzyme production and biochemical reactions, and the bottom box shows how Beadle's experiments affected the normal biochemical process. In this figure, each box represents the borders of the cell, and the dashed lines inside the box represent the nucleus. In the normal cell depiction, three genes (represented as colored rectangles) in the nucleus influence the production of three corresponding enzymes (represented as colored squares). The collections of black circles, orange triangles, green squares, and purple circles represent organic molecules, which the enzymes affect through metabolic reactions. In the normal box, gene 3 somehow produces enzyme 3, which catalyzes a reaction in which the first two molecules combine to form a larger molecule. Enzyme 2 catalyzes the second step in the reaction in which the enzyme modifies the chemical composition of the molecule. Enzyme 3 catalyzes the third step in the reaction in which a carbon atom is added to the molecule. This figure also represents an abnormal process (bottommost box) of enzyme production and biochemical reactions. In the abnormal process, X-rays damaged gene 2, preventing the production of enzyme 2. As a result, neither the second nor the third steps of the chemical reaction can occur.

Thomas Joseph King Jr. was a developmental biologist who, with fellow scientist Robert Briggs, pioneered a method of transplanting nuclei from blastula cells into fresh egg cells lacking nuclei. This method, dubbed nuclear transplantation, facilitated King's studies on cancer cell development. King's work was instrumental for the development of cloning of fish, insects, and mammals.

Published in 1971, Adenocarcinoma of the Vagina: Association of Maternal Stilbestrol Therapy with Tumor Appearance in Young Women, by Arthurs L. Herbst and colleagues, was the first piece of literature connecting maternal use of the drug diethylstilbestrol (DES), also called stilbestrol, with the development of a rare and severe form of vaginal cancer in young women. Diethylstilbestrol was later classified as an endocrine disruptor, a substance that disrupts the hormonal function of the body in those exposed to it during development or later in life. After Herbst and his team established the connection between DES and the occurrence of breast cancer, cervical cancer, infertility, and reproductive abnormalities, the US federal government banned use the drug for pregnant women. The article was published in the New England Journal of Medicine.

Edward Charles Dodds researched the function and effects of natural and artificial hormones on the endocrine system in England during the twentieth century. Though he first worked with hormones such as insulin, Dodds focused on the effects of estrogen in the body and how to replicate those effects with artificial substances. In 1938, along with chemist Robert Robinson, Dodds synthesized the first synthetic estrogen called diethylstilbestrol. Despite the wide use of diethylstilbestrol to treat a variety of hormonal problems like miscarriages during pregnancy and menopause, Dodds argued against the use of synthetic substances in the human body due to their unknown effects. Just before Dodds's death, his hypotheses were confirmed when researchers showed that people exposed to diethylstilbestrol often developed cancer. Dodds was one of the first researchers to investigate the endocrine or hormone system in humans, and his research led to the creation of other synthetic hormones used in contraceptive pills and hormone replacements.

Boris Ephrussi and George Wells Beadle developed a transplantation technique on flies, Drosophila melanogaster, which they described in their 1936 article A Technique of Transplantation for Drosophila. The technique of injecting a tissue from one fly larva into another fly larva, using a micropipette, to grow that tissue in the second larvae, was a means for investigating development of Drosophila. Through this technique, Beadle and Ephrussi studied the role of genes in embryological processes. Beadle and Ephrussi were the first to apply the transplantation method, which had previously been used in the study of larger insects, to the smaller sized Drosophila. Beadle and Ephrussi used this method of transplantation to determine if parts of the optic disc, the section of a larvae that later become the eye buds in the adult, could be extracted from one larva and transplanted into another. They later built upon this research to relate the production of molecules in cells to gene function.

In April 1953, James Watson and Francis Crick published “Molecular Structure of Nucleic Acids: A Structure of Deoxyribose Nucleic Acid” or “A Structure for Deoxyribose Nucleic Acid,” in the journal Nature. In the article, Watson and Crick propose a novel structure for deoxyribonucleic acid or DNA. In 1944, Oswald T. Avery and his group at Rockefeller University in New York City, New York published experimental evidence that DNA contained genes, the biological factors called genes that dictate how organisms grow and develop. Scientists did not know how DNA’s function led to the passage of genetic information from cell to cell, or organism to organism. The model that Watson and Crick presented connected the concept of genes to heredity, growth, and development. As of 2018, most scientists accept Watson and Crick’s model of DNA presented in the article. For their work on DNA, Watson and Crick shared the 1962 Nobel Prize in Physiology or Medicine with Maurice Wilkins.

In 2012, a team of scientists across the US conducted an experiment to find the mechanism that allowed a group of flatworms, planarians, to regenerate any body part. The group included Danielle Wenemoser, Sylvain Lapan, Alex Wilkinson, George Bell, and Peter Reddien. They aimed to identify genes that are expressed by planarians in response to wounds that initiated a regenerative mechanism. The researchers determined several genes as important for tissue regeneration. The investigation helped scientists explain how regeneration is initiated and describe the overall regenerative mechanism of whole organisms.

Sindell v. Abbott Laboratories was a 1980 California case that established the doctrine of market share liability for personal injury cases. For such liability, when a drug causes personal injury and the manufacturer of the drug cannot be identified, each producer is responsible for paying the settlement in proportion to the percentage of the market they supplied. Judith Sindell and Maureen Rogers brought the case against the producers of diethylstilbestrol (DES), which their mothers had taken during pregnancy to prevent miscarriage and other complications. Sindell and Rogers alleged that their mothers' ingestions of DES during pregnancy later caused Sindell and Rogers to develop cancers at the onset of puberty, but they could not identify the specific manufacturer of the drug. The market share liability ruling in Sindell allowed millions of DES-affected individuals to seek restitution for reproductive cancers caused by prenatal exposure to DES.

In 1894, William Stewart Halsted published The Results of Operations for the Cure of Cancer of the Breast Performed at the Johns Hopkins Hospital from June, 1889, to January, 1894, in the medical journal Annals of Surgery. In the article, Halsted describes the results from fifty of his operations on women with breast cancer, performed at Johns Hopkins Hospital in Baltimore, Maryland. Those operations involved a surgical procedure Halsted called radical mastectomy, which consists in removing all of the patient’s breast tissue, chest muscle, and underarm lymph nodes. Halsted’s surgery effectively cured breast cancer in a time period when no other effective treatment options were available. The radical mastectomy remained the standard of care from the 1890s to the 1970s as a means of treating a type of reproductive cancer common to women.

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. Throughout the debate, scientists hypothesized different theories about how DNA replicated, but none of the theories had sound experimental data. Stent introduced DNA replication classes that, if present in DNA, would yield distinct experimental results. Conservative, semi-conservative, and dispersive DNA replication categories shaped scientists' research into how DNA replicated, which led to the conclusion that DNA replicated semi-conservatively.