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.

From a developing embryos three primary germ layers, ectoderm (green), mesoderm (pink) and endoderm (yellow), a variety of differentiated cell types and organ systems arise, far more than are shown here. The three primary germ layers are shown during the gastrula stage because they become distinct at the gastrula stage. The germ cells (blue) are pre- cursors to sperm and egg cells, and they are set aside early in development, and are thought to arise from the ectoderm.

During the mid-twentieth century, Virginia Apgar worked as an obstetrical anesthesiologist and gave drugs to women that reduced their pain during childbirth in the US. In 1953, Apgar created a scoring system, called the Apgar score, that uses five measurements, including heart rate and breathing rate. The Apgar score evaluates newborn infants and determines who needs immediate medical attention. Apgar's work helped decrease infant mortality rates. As of 2020, hospitals around the world use the Apgar score.

Rh factor is a protein found on the outside of Rh-positive red blood cells. Rh incompatibility during pregnancy occurs when an Rh-negative mother is pregnant with an Rh-positive fetus. During delivery, the fetus' Rh-positive blood is introduced into the mother’s body. The Rh-negative mother’s body begins to produce antibodies that attack and kill Rh-positive blood cells. Since the crossover of blood normally occurs during delivery, an Rh-negative woman’s first pregnancy is normally not affected. However, the woman’s antibodies may attack a second Rh-positive fetus as those antibodies can cross into the bloodstream and destroy fetal Rh-positive blood cells.

In 2001, the Supreme Court of New Jersey decided a dispute between a divorced couple over cryopreserved preembryos created through in vitro fertilization (IVF) during the coupleÕs marriage. The former wife (J.B.) wanted the preembryos destroyed, while her former husband (M.B.) wanted them to be used for future implantation attempts, such as by an infertile couple. In J.B. v. M.B. (2001), the court declined to force J.B. to become a parent against her will, concluding that doing so would violate state public policy. Instead, the Supreme Court of New Jersey decided that agreements directing the allocation of cryopreserved preembryos will be enforced, unless one party changes his or her mind prior to the preembryosÕ use or destruction. Should a party revoke an earlier decision about the preembryos, New Jersey courts should weigh the partiesÕ interests with special weight given to an individualÕs right to not procreate.

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.

Leonard Hayflick studied the processes by which cells age during the twentieth and twenty-first centuries in the United States. In 1961 at the Wistar Institute in the US, Hayflick researched a phenomenon later called the Hayflick Limit, or the claim that normal human cells can only divide forty to sixty times before they cannot divide any further. Researchers later found that the cause of the Hayflick Limit is the shortening of telomeres, or portions of DNA at the ends of chromosomes that slowly degrade as cells replicate. Hayflick used his research on normal embryonic cells to develop a vaccine for polio, and from HayflickÕs published directions, scientists developed vaccines for rubella, rabies, adenovirus, measles, chickenpox and shingles.

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. Schleiden and Schwann maintained that the cell was the most fundamental unit of life and that the nucleus was the most significant cellular component. Huxley, instead, promoted an epigenetic theory of the cell, for which properties of life emerge from the outer cytoplasm, cell membrane, and wall (the periplast), as opposed to the inner contents of the cell, including the nucleus (the endoplast). Huxley's arguments in The Cell-Theory influenced future scientists about the role of epigenetic processes in embryology and development.

Plastination is a technique for preserving tissues, organs, and whole bodies for medical purposes and public display. Gunther von Hagens invented a form of the method in 1977 at Heidelberg University in Heidelberg, Germany after observing medical students struggle working with cadavers that quickly decomposed. Von Hagens' body models, referred to as plastinates, have since become widely used educational tools not only for those studying anatomy and medicine, but also for the general public. The technique has contributed to the fields of medicine, anatomy, and embryology by accurately preserving tissues for use in research and education.

Rudolf Carl Virchow lived in nineteenth century Prussia, now Germany, and proposed that omnis cellula e cellula, which translates to each cell comes from another cell, and which became and fundamental concept for cell theory. He helped found two fields, cellular pathology and comparative pathology, and he contributed to many others. Ultimately Virchow argued that disease is caused by changes in normal cells, also known as cellular pathology.