Embryo Project Encyclopedia Articles

"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.

This influential opinion by famed jurist Oliver Wendell Holmes, Jr. was copied by courts throughout the United States. For over sixty years, courts refused to recognize a cause of action on behalf of a child who died before or after birth as a result of injuries suffered in the womb because the fetus was considered legally a part of its mother and thus did not possess personhood. This policy changed after the decision in Bonbrest v. Kotz in 1946.

Meiosis, the process by which sexually-reproducing organisms generate gametes (sex cells), is an essential precondition for the normal formation of the embryo. As sexually reproducing, diploid, multicellular eukaryotes, humans rely on meiosis to serve a number of important functions, including the promotion of genetic diversity and the creation of proper conditions for reproductive success. However, the primary function of meiosis is the reduction of the ploidy (number of chromosomes) of the gametes from diploid (2n, or two sets of 23 chromosomes) to haploid (1n or one set of 23 chromosomes). While parts of meiosis are similar to mitotic processes, the two systems of cellular division produce distinctly different outcomes. Problems during meiosis can stop embryonic development and sometimes cause spontaneous miscarriages, genetic errors, and birth defects such as Down syndrome.

The Public Broadcasting Station (PBS) documentary Life's Greatest Miracle (abbreviated Miracle, available at http://www.pbs.org/wgbh/nova/miracle/program.html), is arguably one of the most vivid illustrations of the making of new human life. Presented as part of the PBS television series NOVA, Miracle is a little less than an hour long and was first aired 20 November 2001. The program was written and produced by Julia Cort and features images by renowned Swedish photographer Lennart Nilsson. It comes as a sequel to the award-winning 1983 NOVA production, The Miracle of Life, which exhibits Nilsson's photography as well. The program showcases a combination of graphic animation, endoscopic and microscopic footage, as well as the story of a couple who are expecting a child. It features a number of new technological and scientific developments not present in its prequel, providing additional relevant information. By depicting human development in a clear and fresh manner, Miracle helps shed light on this indispensible aspect of life. Following is a description of the documentary, highlighting the key points of the film and explaining images featured in it.

Sir John Bertrand Gurdon further developed nuclear transplantation, the technique used to clone organisms and to create stem cells, while working in Britain in the second half of the twentieth century. Gurdon's research built on the work of Thomas King and Robert Briggs in the United States, who in 1952 published findings that indicated that scientists could take a nucleus from an early embryonic cell and successfully transfer it into an unfertilized and enucleated egg cell. Briggs and King also concluded that a nucleus taken from an adult cell and similarly inserted into an unfertilized enucleated egg cell could not produce normal development. In 1962, however, Gurdon published results that indicated otherwise. While Briggs and King worked with Rana pipiens frogs, Gurdon used the faster-growing species Xenopus laevis to show that nuclei from specialized cells still held the potential to be any cell despite its specialization. In 2012, the Nobel Prize Committee awarded Gurdon and Shinya Yamanaka its prize in physiology and medicine for for their work on cloning and pluripotent stem cells.

All sexually reproducing, multicellular diploid eukaryotes begin life as embryos. Understanding the stages of embryonic development is vital to explaining how eukaryotes form and how they are related on the tree of life. This understanding can also help answer questions related to morphology, ethics, medicine, and other pertinent fields of study. In particular, the field of comparative embryology is concerned with documenting the stages of ontogeny. In the nineteenth century, embryologist Karl Ernst von Baer famously noted that embryos of different species generally start out with very similar structure and diverge as they progress through development. This similarity allows for the construction of a series of detailed stages exhibited by a range of different organisms (though in reality embryonic development is a continuous, not staggered, process) describing the progression of events that begin with conception.

In Arizona, statutes that protect persons, such as the wrongful death statute, will not be interpreted by the courts to grant personhood status to frozen embryos. The legislature may grant such protection in the statute if it chooses to do so by explicitly defining the word person to include frozen embryos.

In a case of first impression in the state of New York, the highest state court decided that a priori written agreement between progenitors of frozen embryos regarding the disposition of their "pre-zygotes" in the event of divorce is binding. By copying the general result arrived at by the Tennessee Supreme Court in Davis v. Davis in 1992, the New York court magnified the weight of authority in favor of upholding prior written agreements for in vitro fertilization practices.

The process of gastrulation allows for the formation of the germ layers in metazoan embryos, and is generally achieved through a series of complex and coordinated cellular movements. The process of gastrulation can be either diploblastic or triploblastic. In diploblastic organisms like cnidaria or ctenophora, only the endoderm and the ectoderm form; in triploblastic organisms (most other complex metazoans), triploblastic gastrulation produces all three germ layers. The gastrula, the product of gastrulation, was named by Ernst Haeckel in the mid-1870s; the name comes from Latin, where gaster means stomach, and indeed the gut (archenteron) is one of the most distinctive features of the gastrula.