Embryo Project Encyclopedia Articles

In February 1953, Linus Pauling and Robert Brainard Corey, two scientists working at the California Institute of Technology in Pasadena, California, proposed a structure for deoxyribonucleic acid, or DNA, in their article “A Proposed Structure for the Nucleic Acids,” henceforth “Nucleic Acids.” In the article, Pauling and Corey suggest a model for nucleic acids, including DNA, that consisted of three nucleic acid strands wound together in a triple helix. “Nucleic Acids” was published in Proceedings of the National Academy of Sciences shortly after scientists came to the consensus that genes, the biological factors that control how organisms develop, contained DNA. Though scientists proved Pauling and Corey’s model incorrect, “Nucleic Acids” helped scientists understand DNA’s structure and function as genetic material.

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.

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. Delbrück also contributed to the DNA replication debate that culminated in the 1958 Meselson-Stahl experiment, which demonstrated how organisms replicate their genetic information. For his work with phages, Delbrück earned part of the 1969 Nobel Prize for Physiology or Medicine. Delbrück's work helped shape and establish new fields in molecular biology and genetics to investigate the laws of inheritance and development.

In 1954 Max Delbruck published On the Replication of Desoxyribonucleic Acid (DNA) to question the semi-conservative DNA replication mechanism proposed that James Watson and Francis Crick had proposed in 1953. In his article published in the Proceedings of the National Academy of Sciences, Delbrück offers an alternative DNA replication mechanism, later called dispersive replication. Unlike other articles before it, On the Replication presents ways to experimentally test different DNA replication theories. The article sparked a debate in the 1950s over how DNA replicated, which culminated in 1957 and 1958 with the Meselson-Stahl experiment supporting semi-conservative DNA replication as suggested by Watson and Crick. On the Replication played a major role in the study of DNA in the 1950s, a period of time during which scientists gained a better understanding of DNA as a whole and its role in genetic inheritance.

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.

In June 2017, the Iowa Supreme Court decided the case Plowman v. Fort Madison Community Hospital, or Plowman v. FMCH, and ruled that women who gave birth to children with severe disabilities could sue for wrongful birth in Iowa. Specifically, after Plowman v. FMCH, a woman could sue for wrongful birth if she believed that her physicians failed to disclose evidence of fetal abnormalities that may have prompted her to terminate the pregnancy. Pamela and Jeremy Plowman filed the suit against the Fort Madison Community Hospital in Fort Madison, Iowa, alleging that hospital physicians failed to inform them that a prenatal test showed fetal abnormalities. Plowman v. FMCH gave women in Iowa the legal right to sue if physicians failed to tell them about fetal defects.

William Thomas Astbury studied the structures of fibrous materials, including fabrics, proteins, and deoxyribonucleic acid, or DNA, in England during the twentieth century. Astbury employed X-ray crystallography, a technique in which scientists use X-rays to learn about the molecular structures of materials. Astbury worked at a time when scientists had not yet identified DNA’s structure or function in genes, the genetic components responsible for how organisms develop and reproduce. He was one of the first scientists to use X-ray crystallography to study the structure of DNA. According to historians, Astbury helped establish the field of molecular biology as he connected microscopic changes in the structure of materials to changes in their large-scale properties. Astbury and his images helped scientists to understand the structure of DNA and its role in genetics.

Hormone releasing intrauterine devices or hormonal IUDs are contraceptive devices placed in a woman’s uterus to prevent pregnancy by continuously releasing a low dose of certain hormones. Jouri Valter Tapani Luukkainen, a medical researcher at the University of Helsinki, introduced the first hormonal IUD in 1976. Luukkainen’s IUD was a plastic device shaped like a capital T. The horizontal shafts of the IUD held a reservoir of the hormone Levonorgestrel that the IUD slowly released at a constant rate over the IUD’s lifetime, allowing the hormonal IUD to remain effective for five to seven years. Women can use hormonal IUDs for long term contraception that requires no maintenance on the part of the user. The hormonal IUD provides women an option for reliable long-term birth control that does not require maintenance to remain effective.

In 1944, Oswald Avery, Colin MacLeod, and Maclyn McCarty published an article in which they concluded that genes, or molecules that dictate how organisms develop, are made of deoxyribonucleic acid, or DNA. The article is titled “Studies on the Chemical Nature of the Substance Inducing Transformation of Pneumococcal Types: Induction of Transformation by a Desoxyribonucleic Acid Fraction Isolated from Pneumococcus Type III,” hereafter “Transformation.” The authors isolated, purified, and characterized genes within bacteria and found evidence that those genes were made of DNA and not protein. Though scientists were initially skeptical that genes were made of DNA, they later recognized that the data reported in “Transformation” were clear evidence that DNA was genetic material, a revelation that furthered research about how organisms grow, develop, and pass on traits to offspring.

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. Many scientists, beginning with Max Delbrück, questioned Watson and Cricks’ model and suggested new theories for DNA replication. By 1957, three theories about DNA replication prevailed: semi-conservative, conservative, and dispersive replication. Then, Matthew Meselson and Franklin Stahl conducted the Meselson-Stahl experiment, which returned results that supported the semi-conservative theory of DNA replication. The collaboration among scientists that ultimately produced concrete evidence of the DNA replication mechanism furthered both theoretical and physical explanations of genetics and molecular biology, providing insight into how life develops, reproduces, and evolves.