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| 22.1 Genome Sequencing: A Continuation of Genetics 1. The human genome project involves the assembly of a DNA sequence map for the 3 billion base pairs present in all 23 human chromosomes. 2. Two groups, the International Consortium and Celera Genomics, used two opposite strategies to obtain a draft sequence of the human genome. 3. The use of bacterial artificial chromosomes (BACs), shotgun clones, and positional cloning has yielded a detailed look at the human genome and is facilitating the identification of disease causing genes. 22.2 The Origin of the IdeaThe Sanger Method of DNA Sequencing 1. The Sanger method of DNA sequencing involves an enzymatic extension reaction to generate complementary copies of an unknown DNA sequence. 2. Incorporation of "dideoxy" base causes chain termination and separation of extension products on polyacrylamide gels reveals the sequence bases in the unknown DNA. 3. DNA sequencing occurs on a vast scale today through the use of automated DNA sequencing machines. The Project Starts 1. The idea to sequence the human genome emerged in the mid 1980s. 2. The project officially began in 1990, switched from mapping to sequencing in 1995, and by 1999 competition between private and public efforts intensified. 22.3 Technology Drives the Sequencing Effort 1. Expressed sequenced tags (EST) technology enabled researchers to focus on protein encoding genes. 2. The speed of the project depended upon the technological developments of automated DNA sequencing machines and DNA sequence alignment computer software. 22.4 Genome Information Answers and Raises QuestionsNonhuman Genome Projects 1. Mycoplasm genitalium has the smallest known genome and represents a "near-minimal set of genes for independent life." 2. Large percentages of the known genomes have an unknown function. 3. Comparing genomes of different species indicates shared ancestry. 4. Homologies between human genes and genes of other organisms may allow the other organisms to serve as test-beds for human therapies. |