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GENETIC ENGINEERING: CHAPTER 9 CHANGING THE WORLD Selective Breeding o Allows only those organisms with desired characteristics to produce the next generation. o Nearly all domestic animals and most crop plants have been produced by selective breeding. Hybridization o Crossing of dissimilar individuals to bring together the best of both organisms. o Hybrids, the individuals produced by such crosses, are often hardier than either of the parents. Inbreeding o Continued breeding of individuals with similar characteristics. o Helps to ensure that characteristics that make each breed unique will be preserved. o Serious genetic problems can result from excessive inbreeding. Increasing Variation o Accomplished by inducing mutations into a population o Mutations occur spontaneously, but breeders can increase the mutation rate by using radiation and chemicals. o Breeders can often produce a few mutants with desirable characteristics that are not found in the original population. o Beneficial? Introducing mutations has allowed scientists to develop hundreds of useful bacterial strains, including bacteria that can clean up oil spills. Mutations in some plant cells produce cells that have double or triple the normal number of chromosomes. This condition, known as polyploidy, produces new species of plants that are often larger and stronger than their diploid relatives. Polyploidy in animals is usually fatal. MANIPULATING DNA Scientists use different kinds of techniques to: o extract DNA from cells o cut DNA into smaller pieces o identify the sequence of bases in a DNA molecule o make unlimited copies of DNA Genetic Engineering: o biologists make changes in the DNA code of a living organism DNA Extraction o The cells are opened and the DNA is separated from the other cell parts through a simple chemical procedure Cutting DNA o Most DNA molecules are too large to be analyzed, so biologists cut them into smaller fragments using restriction enzymes o Each restriction enzyme cuts DNA at a specific sequence of nucleotides. Separating DNA o In gel electrophoresis, DNA fragments are placed at one end of a porous gel, and an electric voltage is applied to the gel First, restriction enzymes cut DNA into fragments. The DNA fragments are poured into wells on a gel. An electric voltage is applied to the gel. The smaller the DNA fragment, the faster and farther it will move across the gel. o “Reading” DNA: Southern Blotting In genetically modified organisms, Southern blots are used to make certain that the necessary section of DNA has been inserted into the genome of the organism being modified Steps: DNA is separated from its source and cut with a restriction enzyme The fragments are put into a gel and sorted by electrophoresis in order of length, the shortest at the top and the longest at the bottom A chemical is used to make the fragments visible, and the DNA is moved from the gel on to a nylon membrane A radioactive probe is added, which attaches to complementary DNA fragments The nylon membrane is then covered with an X-ray film which, once developed, reveals the position of the probe Making Copies of DNA o Polymerase chain reaction (PCR) is a technique that allows biologists to make copies of genes. o Small amounts of DNA can be multiplied making it easier to analyze. o Made possible by an enzyme found in a bacterium living in hot springs in Yellow Stone National Park. CELL TRANSFORMATION Transforming Bacteria o During transformation, a cell takes in DNA from outside the cell. The external DNA becomes a part of the cell's DNA o Steps: Foreign DNA is first joined to a small, circular DNA molecule known as a plasmid. Found naturally in some bacteria Very useful for DNA transfer. Contains a genetic marker Gene that makes it possible to distinguish bacteria that carry the plasmid (and the foreign DNA) from those that don't. How can you tell if a transformation has been successful? o The recombinant DNA is integrated into one of the chromosomes of the cell. Bacteria: o A certain bacterium exists that produces tumors in plant cells. o Researchers inactivate the tumor-producing gene found in this bacterium and insert a piece of foreign DNA into the plasmid. o The recombinant plasmid can then be used to infect plant cells. Plants: o When their cell walls are removed, plant cells in culture will sometimes take up DNA on their own. o DNA can also be injected directly into some cells. o Cells transformed by either procedure can be cultured to produce adult plants. Animals: o Many egg cells are large enough that DNA can be directly injected into the nucleus. o Enzymes may help to insert the foreign DNA into the chromosomes of the injected cell. o DNA molecules used for transformation of animal and plant cells contain marker genes. o DNA molecules can be constructed with two ends that will sometimes recombine with specific sequences in the host chromosome. o The host gene normally found between those two sequences may be lost or replaced with a new gene. APPLICATIONS OF GENETIC ENGINEERING Transgenic Organisms o An organism described as transgenic, contains genes from other species. o Uses Microorganisms Transgenic bacteria produce important substances useful for health and industry. Inexpensive Easy to manufacture Have been used to produce: o insulin o growth hormone o clotting factor Animals Have been used to study genes and improve the food supply. Mice have been produced with human genes that make their immune systems act like those of humans. Allows scientists to study the effects of diseases on the human immune system without having to study them ON humans. Researchers are trying to produce transgenic chickens that to be resistant to bacterial infections that cause food poisoning. Plants Transgenic plants are now an important part of our food supply. Many of these plants contain a gene that produces a natural insecticide, so plants don’t have to be sprayed with pesticides. Cloning o A clone is a member of a population of genetically identical cells produced from a single cell. o In 1997, Ian Wilmut cloned a sheep called Dolly