Embryo Project Encyclopedia

The US 2nd Circuit Court of Appeals' 1984 decision United States v. University Hospital, State University Hospital of New York at Stony Brook set a significant precedent for affirming parental privilege to make medical decisions for handicapped newborns, while limiting the ability of the federal government to intervene. The ruling stemmed from the 1983 case involving an infant born with severe physical and mental congenital defects; the infant was only identified as Baby Jane Doe. After her parents opted against corrective surgery for some of her deformities, Baby Jane Doe became the epicenter of a national right-to-life debate that had been previously sparked one year prior with the case of Baby Doe, an Indiana infant born with similarly severe handicaps.

The Baby Doe Rules represent the first attempt by the US government to directly intervene in treatment options for neonates born with congenital defects. The name of the rule comes from the controversial 1982 case of a Bloomington, Indiana infant Baby Doe, a name coined by the media. The Baby Doe Rules mandate that, as a requirement for federal funding, hospitals and physicians must provide maximal care to any impaired infant, unless select exceptions are met. If a physician or parent chooses to withhold full treatment when the exceptions are not met, they are liable for medical neglect. After a prolonged legal battle, President Ronald Reagan signed the law on 9 October 1984 as an amendment to the Child Abuse Prevention and Treatment Act (CAPTA) of 1974. Since then, the Baby Doe Rules have influenced both the parents' right to make medical decisions for their child and the way laws can affect treatment options in the US.

The French flag model represents how embryonic cells receive and respond to genetic information and subsequently differentiate into patterns. Created by Lewis Wolpert in the late 1960s, the model uses the French tricolor flag as visual representation to explain how embryonic cells can interpret genetic code to create the same pattern even when certain pieces of the embryo are removed. Wolpert's model has provided crucial theoretical framework for investigating universal mechanisms of pattern formation during development.

Fetus in fetu is a rare variety of parasitic twins , where the developmentally abnormal parasitic twin is completely encapsulated within the torso of the otherwise normally developed host twin. In the late eighteenth century, German anatomist Johann Friedrich Meckel was the first to described fetus in fetu, which translates to “fetus within fetus.” Fetus in fetu is thought to result from the unequal division of the totipotent inner cell mass , the mass of cells that is the ancestral precursor to all cells in the body. The unequal division is thought to occur during the formation of the blastocyst, which can also result in parasitic and conjoined twins . Fetus in fetu represents a developmental anomaly that has prompted developmental biologists to further examine the mechanisms for how twins arise.

Christiane Nusslein-Volhard studied how genes control embryonic development in flies and in fish in Europe during the twentieth and twenty-first centuries. In the 1970s, Nusslein-Volhard focused her career on studying the genetic control of development in the fruit fly Drosophila melanogaster. In 1988, Nusslein-Volhard identified the first described morphogen, a protein coded by the gene bicoid in flies. In 1995, along with Eric F. Wieschaus and Edward B. Lewis, she received the Nobel Prize in Physiology or Medicine for the discovery of genes that establish the body plan and segmentation in Drosophila. Nusslein-Volhard also investigated the genetic control of embryonic development to zebrafish, further generalizing her findings and helping establishing zebrafish as a model organism for studies of vertebrate development.

For more than 2000 years, embryologists, biologists, and philosophers have studied and detailed the processes that follow fertilization. The fertilized egg proliferates into cells that begin to separate into distinct, identifiable zones that will eventually become adult structures through the process of morphogenesis. As the cells continue to multiply, patterns form and cells begin to differentiate, and eventually commit to their fate. This progression of events can be examined by following the developmental path of each progenitor cell and creating a two-dimensional representation where cell location and fate can be labeled and marked. Fate mapping is a method for tracing cell lineages and a fundamental tool of developmental biology and embryology.

Early development occurs in a highly organized and orchestrated manner and has long attracted the interest of developmental biologists and embryologists. Cell lineage, or the study of the developmental differentiation of a blastomere, involves tracing a particular cell (blastomere) forward from its position in one of the three germ layers. Labeling individual cells within their germ layers allows for a pictorial interpretation of gastrulation. This chart or graphical representation detailing the fate of each part of an early embryo is referred to as a fate map. In essence, each fate map portrays the developmental history of each cell.

Gastrulation is an early stage in embryo development in which the blastula reorganizes into three germ layers: the ectoderm, the mesoderm, and the endoderm. Gastrulation occurs after cleavage but before neurulation and organogenesis. Ernst Haeckel coined the term; gaster, meaning stomach in Latin, is the root for gastrulation, as the gut is one of the most unique creations of the gastrula.

A node, or primitive knot, is an enlarged group of cells located in the anterior portion of the primitive streak in a developing gastrula. The node is the site where gastrulation, the formation of the three germ layers, first begins. The node determines and patterns the anterior-posterior axis of the embryo by directing the development of the chordamesoderm. The chordamesoderm is a specific type of mesoderm that will differentiate into the notochord, somites, and neural tube. Those structures will later form the vertebral column. In the chick embryo, the node is referred to as Hensen's node because of its discoverer, Viktor Hensen, who first described the node in 1875. The discovery of Hensen's node has helped to answer questions of axis formation and has allowed experimental embryologists to further investigate vertebrate embryonic development.

Through various studies developmental biologists have been able to determine that the muscles of the back, ribs, and limbs derive from somites. Somites are blocks of cells that contain distinct sections that diverge into specific types (axial or limb) of musculature and are an essential part of early vertebrate development. For many years the musculature of vertebrates was known to derive from the somites, but the exact developmental lineage of axial and limb muscle progenitor cells remained a mystery until Nicole Le Douarin and Charles P. Ordahl published "Two Myogenic Lineagues within the Developing Somite" in 1991. This paper describes their experiment, which used chick-quail chimeras to demonstrate the exact lineage of the limb and back musculature.