Human Develop (Your Body) (Your Body, How It Works)
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Provides an overview of human development, discussing fertilization, cell development, and cell movement.
of cells called the hypoblast delaminates from the inner cell mass (Figure 5.1). These cells migrate and divide to line the blastocoel, and the newly lined cavity is called the yolk sac. Like the trophoblast, the yolk sac is actually considered to be an extra-embryonic tissue. As development proceeds, the yolk sac will become an extension of the developing gut of the embryo. As the hypoblast is forming, the cells of the inner cell mass that remain, and do not contribute to the hypoblast, become
this lineage of cells will give rise to include the skin and central nervous system. CONNECTIONS During the process of gastrulation, the cells of the embryo undergo significant morphogenetic movements that result in the establishment of the germ layers. The layers will continue to differentiate during development to give rise to more than 200 different types of cells that make up a human. Each of these germ layers is positioned in a manner consistent with the body plan of a human. The ectoderm
example. The identification of the gene that, when mutated, leads to the malformations associated with this syndrome will also identify a gene that is likely involved in limb and cranio-facial development. Model organisms are often manipulated experimentally to mutate specific genes so that the effect of these mutations, and therefore the role of the genes, can be examined. Certain model organisms, such as Drosophila and zebrafish, have also been subjected to mutagenetic screens. In these types
Special Issue. “The Human Genome.” 16 February 2001. Vol. 291 (#5507). 1145-1434. Nova Special: “Life’s Greatest Miracle.” Originally broadcast November 20, 2001 (also see http://www.pbs.org/wgbh/nova/miracle/). Websites Medline Plus, part of the U.S. National Institutes of Health and the National Library of Medicine. Information on Birth Defects. http://www.nlm.nih.gov/medlineplus/birthdefects.html Illinois Teratogen Information Service, information on teratogens and human development.
These roles of DNA are primarily accomplished by it acting as instructions for making proteins. Proteins are molecules that carry out the majority of cellular functions. The importance of proteins in relationship to the functions of the cell is reflected in CLONING BY NUCLEAR TRANSFER Recently, the possibility of producing organisms either asexually or by cloning has received a great deal of media attention. In 1997, biologists in Scotland announced the birth of Dolly the sheep. Dolly was the