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Chapter 21 - Chapter 21 The Genetic Basis of Development...

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Chapter 21 - The Genetic Basis of Development Chapter 21 The Genetic Basis of Development Lecture Outline Overview: From Single Cell to Multicellular Organism The application of genetic analysis and DNA technology to the study of development has brought about a revolution in our understanding of how a complex multicellular organism develops from a single cell. o In 1995, Swiss researchers identified a gene that functions as a master switch to trigger the development of the eye in Drosophila. A similar gene triggers eye development in mammals. o Developmental biologists are discovering remarkable similarities in the mechanisms that shape diverse organisms. While geneticists were advancing from Mendel’s laws to an understanding of the molecular basis of inheritance, developmental biologists were focusing on embryology. o Embryology is the study of the stages of development leading from fertilized egg to fully formed organism. In recent years, the concepts and tools of molecular genetics have reached a point where a real synthesis of genetics and developmental biology has been possible. When the primary research goal is to understand broad biological principles, the organism chosen for study is called a model organism. o Researchers select model organisms that are representative of a larger group, suitable for the questions under investigation, and easy to grow in the lab. For study of the connections between genes and development, suitable model organisms have short generation times and small genomes that are suitable for genetic analysis. o Model organisms used in developmental genetics include the fruit fly Drosophila melanogaster, the nematode Caenorhabditis elegans, the mouse Mus musculus, the zebra fish Danio rerio, and the plant Arabidopsis thaliana. The fruit fly Drosophila melanogaster was first chosen as a model organism by geneticist T. H. Morgan and intensively studied by generations of geneticists after him. o The fruit fly is small and easily grown in the laboratory. o It has a generation time of only two weeks and produces many offspring. o Embryos develop outside the mother’s body. o There are vast amounts of information on its genes and other aspects of its biology. o However, because first rounds of mitosis occur without cytokinesis, parts of its development are superficially quite different from that of other organisms. o Sequencing of the Drosophila genome was completed in 2000.
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It has 180 × 106 base pairs (180 Mb) and contains about 13,700 genes. The nematode Caenorhabditis elegans normally lives in the soil but is easily grown in petri dishes. o Only a millimeter long, it has a simple, transparent body with only a few cell types and grows from zygote to mature adult in only three and a half days.
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