Embryo Project Encyclopedia Articles

Rosalind Elsie Franklin worked with X-ray crystallography at King's College London, UK, and she helped determine the helical structure of DNA in the early 1950s. Franklin's research helped establish molecular genetics, a field that investigates how heredity works on the molecular level. The discovery of the structure of DNA also made future research possible into the molecular basis of embryonic development, genetic disorders, and gene manipulation.

Endoderm is one of the germ layers-- aggregates of cells that organize early during embryonic life and from which all organs and tissues develop. All animals, with the exception of sponges, form either two or three germ layers through a process known as gastrulation. During gastrulation, a ball of cells transforms into a two-layered embryo made of an inner layer of endoderm and an outer layer of ectoderm. In more complex organisms, like vertebrates, these two primary germ layers interact to give rise to a third germ layer, called mesoderm. Regardless of the presence of two or three layers, endoderm is always the inner-most layer. Endoderm forms the epithelium-- a type of tissue in which the cells are tightly linked together to form sheets-- that lines the primitive gut. From this epithelial lining of the primitive gut, organs like the digestive tract, liver, pancreas, and lungs develop.

"Induction and Patterning of the Primitive Streak, an Organizing Center of Gastrulation in the Amniote," (hereafter referred to as "Induction") examines the mechanisms underlying early amniote gastrulation and the formation of the primitive streak and midline axis. The review, authored by Takashi Mikawa and colleagues at Cornell University Medical College, was published in Developmental Dynamics in 2004. The article primarily discusses chick embryos as a model organism for nonrodent amniote gastrulation, although it intermittently touches on nonamniote gastrulation for comparative purposes. "Induction" attempts to explain the initiation of cell differentiation and embryo organization, one of the most intriguing processes of embryology.

Hilde Proscholdt Mangold was a doctoral student at the Zoological Institute at the University of Freiburg in Freiburg, Germany, from 1920-1923. Mangold conducted research for her dissertation 'On the Induction of Embryonic Primordia by Implantation of Organizers from Different Species' ('Ueber Induktion von Embryonanlagen durch Implantation artfremder Organisatoren'), under the guidance of Hans Spemann, a professor of zoology at the University of Freiburg. The dissertation was the culmination of five experiments on three species of newt embryos, of the genus Triton (presently, Triturus), performed during the summers of 1921 and 1922, which resulted in a confirmation of Spemann's organizer concept. Spemann and Mangold published the dissertation in a 1924 edition of Roux's Archives for Microscopic Anatomy and Developmental Mechanics (Roux's Archiv fur Mikroskopische Anatomie und Entwicklungsmechanik)."

Calvin Blackman Bridges studied chromosomes and heredity in the US throughout the early twentieth century. Bridges performed research with Thomas Hunt Morgan at Columbia University in New York City, New York, and at the California Institute of Technology in Pasadena, California. Bridges and Morgan studied heredity in Drosophila, the common fruit fly. Throughout the early twentieth century, researchers were gathering evidence that genes, or what Gregor Mendel had called the factors that control heredity, are located on chromosomes. At Columbia, Morgan disputed the theory, but in 1916, Calvin Bridges published evidence that, according to Morgan, did much to convince skeptics of that theory. Bridges also established that specific chromosomes function in determining sex in Drosophila.

Alfred Henry Sturtevant studied heredity in fruit flies in the US throughout the twentieth century. From 1910 to 1928, Sturtevant worked in Thomas Hunt Morgan’s research lab in New York City, New York. Sturtevant, Morgan, and other researchers established that chromosomes play a role in the inheritance of traits. In 1913, as an undergraduate, Sturtevant created one of the earliest genetic maps of a fruit fly chromosome, which showed the relative positions of genes along the chromosome. At the California Institute of Technology in Pasadena, California, he later created one of the first fate maps, which tracks embryonic cells throughout their development into an adult organism. Sturtevant’s contributions helped scientists explain genetic and cellular processes that affect early organismal development.

From 1913 to 1916, Calvin Bridges performed experiments that indicated genes are found on chromosomes. His experiments were a part of his doctoral thesis advised by Thomas Hunt Morgan in New York, New York. In his experiments, Bridges studied Drosophila, the common fruit fly, and by doing so showed that a process called nondisjunction caused chromosomes, under some circumstances, to fail to separate when forming sperm and egg cells. Nondisjunction, as described by Bridges, caused sperm or egg cells to contain abnormal amounts of chromosomes. In some cases, that caused the offspring produced by the sperm or eggs to display traits that they would typically not have. His research on nondisjunction provided evidence that chromosomes carry genetic traits, including those that determine the sex of an organism.

In 1910, Thomas Hunt Morgan performed an experiment at Columbia University, in New York City, New York, that helped identify the role chromosomes play in heredity. That year, Morgan was breeding Drosophila, or fruit flies. After observing thousands of fruit fly offspring with red eyes, he obtained one that had white eyes. Morgan began breeding the white-eyed mutant fly and found that in one generation of flies, the trait was only present in males. Through more breeding analysis, Morgan found that the genetic factor controlling eye color in the flies was on the same chromosome that determined sex. That result indicated that eye color and sex were both tied to chromosomes and helped Morgan and colleagues establish that chromosomes carry the genes that allow offspring to inherit traits from their parents.

In 1913, Alfred Henry Sturtevant published the results of experiments in which he showed how genes are arranged along a chromosome. Sturtevant performed those experiments as an undergraduate at Columbia University, in New York, New York, under the guidance of Nobel laureate Thomas Hunt Morgan. Sturtevant studied heredity using Drosophila, the common fruit fly. In his experiments, Sturtevant determined the relative positions of six genetic factors on a fly’s chromosome by creating a process called gene mapping. Sturtevant’s work on gene mapping inspired later mapping techniques in the twentieth and twenty-first centuries, techniques that helped scientists identify regions of the chromosome that when mutated cause organisms to develop abnormally and to create treatments to cure those kinds of disorders.

Kurt Benirschke studied cells, placentas, and endangered species in Germany and the US during the twentieth century. Benirschke was professor at the University of California in San Diego, California, and a director of the research department at the San Diego Zoo in San Diego, California. He also helped form the research department of the San Diego Zoo and its sister organization, the Center for Reproduction of Endangered Species. Benirschke contributed to the field of embryology through his work on human and animal reproduction, including work on human placentas and birth defects, through work on the structure of chromosomes, and through work on the reproduction and conservation of endangered species.