Chapter 15 THE HUMAN GENOME PROJECT AND GENOMICS

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1 Chapter 15 THE HUMAN GENOME PROJECT AND GENOMICS Chapter Summary Mapping of human genes means identifying the chromosome and the position on that chromosome where a particular gene is located. Initially this was accomplished by looking at large families and seeing which two traits were inherited tighter (linked). Linkage studies showed which genes were located together on the same chromosome, and how far apart they were located. Information on human genes accumulated slowly from linkage studies. Mapping the genes of experimental organisms by linkage studies yielded more information. These organisms could be mated in a planned manner and their large families analyzed. The next step involved mapping genetic markers on the chromosome rather than genes. Genes could be mapped much more precisely based on their inheritance with one of these markers, and the number of mapped genes rose dramatically. The Human Genome Project had the ambitious goal of determining the sequence of DNA nucleotides for one set of human chromosomes. (Recall that a set is one of each kind of chromosome, and includes one member of each gene pair.) With this information, computers could locate genes by telltale sequences. In this way, the branch of genetics known as genomics developed. Since 1990, 125 species (including humans) have had their genomes sequenced. An enormous amount of information on genes and their proteins has become available and is currently being mined by geneticists, using computers.

2 120 Chapter 15 The search for human genes has not ended with the production of a DNA sequence. It is necessary to separate genes from pseudogenes and spacer DNA. Once a gene is located, the amino acid sequence of its protein can be determined, and a comparison can be made of normal and abnormal proteins. With this information in hand, the way the abnormal protein influences the phenotype may be uncovered, and drugs to counteract the abnormal protein may be developed. In addition, the Human Genome Project produced many surprises for geneticists, such as the small total number of human genes, the numerical relationship between genes and proteins, and the similarity of genes in very different organisms. The next major task for geneticists is to explain the information about proteins that can be learned from knowing a gene s sequence. Many genes can produce multiple proteins instead of just one. Sequences of amino acids within those proteins may give clues to the function of the protein. Some proteins discovered so far do not fall into any known functional category. The remark has been made that compared with proteomics, Genes were easy. The explosion of genetic information has created the usual set of ethical, legal, and social problems that have occurred with most major scientific advances. Just as genetics is an interesting subject because we can easily apply the information to ourselves and our families, information about us and our families could be available to a large number of interested people and corporations at the touch of a computer key. The right to privacy will come in conflict with real or perceived rights of other individuals and organizations. Learning Objectives When you have assimilated the information in this chapter, you should feel competent to discuss the following: a. the various methods that have been used to map human genes. b. the types of information the Human Genome Project has provided. c. the types of information that should become available from mining the human genome databases. d. the ways in which human genome information can be used to study human disorders. e. ethical, social, and legal problems that are created by having so much information available.

3 The Human Genome Project and Genomics 121 Key Terms linkage centimorgan positional cloning genomics bioinformatics clone-by-clone method shotgun sequencing annotation open reading frame proteomics Multiple Choice Circle the letter of the best answer. 1. The primary purpose of the Human Genome Project has been to a. promote international cooperation among scientists b. prove the genetic superiority of humans c. map all the genes of humans d. use technology to improve the genetic makeup of humans 2. According to the chapter introduction, grants and a $500,000 prize have been offered to reduce the cost of sequencing a human genome to $1000. The relatively low cost should a. help pay off the national debt b. allow the development of do-it-yourself home genome sequence kits c. permit genome sequencing to become part of routine health care d. boost Internet sales of chemicals 3. In early attempts to map human genes a. Bell and Haldane developed DNA sequencing b. The hemophilia gene was mapped to chromosome #9 c. Bell and Haldane discovered they each had genetic disorders d. X-linked traits were shown to be inherited together 4. Linked genes a. are located on the same chromosome b. can assort independently c. are always found on the X chromosome d. must involve blood type

4 122 Chapter Recessive X-linked genes can be identified because of their patterns of inheritance. This pattern is a. affected father to affected son b. unaffected mother to affected son c. affected mother to unaffected daughter d. found more often in females than in males 6. If two linked genes have a cross-over rate of 14 percent, they are located? on the chromosome. a. 14 nucleotides apart b. very close to each other c. 14 map units apart d. 7 centimorgans apart 7. Linkage studies resulted in genetic maps of mice, corn, and bacteria. Human maps lagged behind because the studies require a. large families with two genetic disorders b. genetic counselors to draw the pedigrees c. marriages regulated by the government d. brother-sister marriages 9. Positional cloning a. had a lower success rate in mapping human genes than did linkage studies b. is slow and gives unreliable results c. combined linkage with genetic markers d. was the brain-child of J. Craig Venter 10. According to the diagram in Figure 15.13, the largest group of human genes with a known molecular function codes for a. nucleic acid enzymes b. signaling molecules c. cytoskeletal proteins d. receptors e. transcription factors

5 The Human Genome Project and Genomics Analysis of the human genome sequence information has shown a. humans have 80, ,000 genes b. different mutations in a single gene can give rise to different genetic disorders c. genes are evenly distributed across our 24 different chromosomes d. approximately 75 percent of our DNA encodes genetic information