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Chapter SummaryDevelopmental Biology is the study of how multicellular organisms grow and mature. Both plants and animals have a developmental program they must go through to become a fertile adult. The process of development can be similar or dissimilar in different organisms. In this text we will describe development in different species and investigate the molecular mechanisms behind development. During development a fertilized egg becomes an adult through a series of non-equivalent cell divisions. Non-equivalent cell divisions occur when a dividing cell produces two daughter cells that are qualitatively different from each other. These non-equivalent cell divisions create different cell types each achieving different fates. For example, by the end of development we have skin cells, nerve cells, muscle cells, and many other cells types each having different fates. We call these cell types specialized cells. The fate of different cell types may be a product of lineage or position in the embryo. Lineage differences are the result of differential inheritance of cytoplasm by two daughter cells during mitosis. Positional differences are the result of two daughter cells occupying different cellular environments and receiving different types of signals from that environment. During development cells receive signals from other cells surrounding them. During cell signaling, a signal is transduced from the outside of the cell to the inside of the cell. This is the process of signal transduction. Signal transduction begins when a signaling molecule, or ligand, binds to a receptor at the cell surface. This promotes a change in the receptor that may activate a second messenger inside the cell. The second messenger may enter the nucleus to activate gene transcription. The result of signal transduction is usually a change in transcription. We can also learn about the process of specialization by studying regeneration. Regeneration is the process by which new tissue is created from specialized, pre-programmed adult tissue. During regeneration, adult cells despecialize and respecialize into many new cell types. Regeneration occurs in plants and in some animals like salamanders, flatworms and segmented worms. Studying regeneration can help us to understand how cells are programmed during development. One of the most important things to understand about development is that all cells in an embryo are genetically identical. The different cell types produced during development are not caused by differential inheritance of genetic material. One of the big questions of development is how cells become different from each other without changing their genetic material. Differentiation is the process by which cells acquire different fates as a result of differences in the expression of a constant genome. This is one of the dominant principles of modern developmental biology. Further ReadingTo study Developmental Biology, it is essential to have an understanding of basic cell biology, molecular biology and genetics. Here are some textbook references for review: Cell Biology , Pollard Molecular Biology of the Cell , Alberts Genetics , Hartwell If you want a good resource to investigate the field of developmental biology, visit the Society for Developmental Biology’s website at http://sdb.bio.purdue .edu/. The Society for Developmental Biology supports education and research of developmental biology, and is the premier society for developmental biologists. Their site has many useful resources, including pictures, movies and educational resources. The society also publishes the monthly peer reviewed scientific journal Developmental Biology. The Roslin Institute, located in Edinburgh Scotland, is where Dolly was cloned. They emphasize research in animals important for agriculture and advancements in cloning methods for the agricultural industry. If you want to find out how modern developmental biology intersects with agriculture and business, visit their website at http ://www.ri.bbsrc.ac.uk/. One of the interesting things about Dolly is that she died a premature death. Some have proposed that all clones will suffer from premature aging, and this has been a controversial aspect of cloning. Read Dolly’s obituary published in nature http://www.nature.com/nsu/030217/030217-6.html. Here is the original article published in Nature describing the cloning of “Dolly” by the Roslin Institute, published 7 March 1996: Campbell , K.H.S., McWhir, J., Ritchie, W.A., & Wilmut, I.* 1996. Sheep cloned by nuclear transfer from a cultured cell line. Nature 380 64-66
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