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CHAPTER 13

CHAPTER 13. GENETIC ENGINEERING. Brain Teaser:. How can a sheep that is 12 years old have an identical twin that is only 4 years old? What is genetic engineering? Do you eat genetically engineered foods? If so what types? Is it possible for bacteria to produce human insulin?

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CHAPTER 13

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  1. CHAPTER 13 GENETIC ENGINEERING

  2. Brain Teaser: • How can a sheep that is 12 years old have an identical twin that is only 4 years old? • What is genetic engineering? • Do you eat genetically engineered foods? If so what types? • Is it possible for bacteria to produce human insulin? • What is cloning? Should we clone humans?

  3. SECTION 1 Changing the Living World

  4. Key Concept Questions • What is the purpose of selective breeding?  • Why might breeders try to induce mutations?

  5. A New Breed • The tomatoes in your salad and the dog in your backyard are a result of selective breeding. • Over thousands of years, humans have developed breeds of animals and plants that have desirable characteristics. • How do breeders predict the results of crossing individuals with different traits?

  6. What would happen if you crossed the following two breeds of dog?

  7. Why do a Chihuahua, a golden retriever, a pug, and a great Dane all look so different but are still the same species?

  8. SELECTIVE BREEDING • Allowing only those organisms with desiredcharacteristics to produce the next generation

  9. What types of organisms have been selectively bred by humans? • horses • dogs • cats • farm animals • most crop plants

  10. We have been manipulating DNA for generations! • Artificial breeding • creating new breeds of animals & new crop plants to improve our food

  11. Animal breeding

  12. Breeding food plants • “Descendants” of the wild mustard • the “Cabbage family”

  13. Breeding food plants Evolution of modern corn (right) from ancestral teosinte (left).

  14. A Brave New World

  15. HYBRIDIZATION • Crossing dissimilar individuals to bring together the best of both organisms • hybrids are often hardier than either of the parents • used widely by farmers • ex) food-producing crop crossed with disease-resistance crop = disease-resistant, food producing crop

  16. INBREEDING • Continued breeding of individuals with similar characteristics • Look at the above pictures • How can you tell that the puppies are inbred? • They all look identical

  17. What differences might these puppies have if they were hybrids? • Different color, fur type, size

  18. What could be the risks of inbreeding? • most of the members of a breed are genetically similar • there is a chance that a cross between these two individuals will bring together two recessive alleles for a genetic defect • In dogs – blindness, joint deformities, susceptibility to diseases such as parvo virus and cancers

  19. Would you use hybridization or inbreeding to produce a homozygous individual? • Inbreeding • How would you make a heterozygous individual? • Hybridization

  20. Selective breeding would be nearly impossible without the wide variation that is found in the natural populations. • This is one of the reasons biologists are interested in preserving the diversity of plants and animals in the wild

  21. What can breeders do if they want more variation than naturally exists in nature? • Breeders can increase the genetic variation in a population by inducing (causing) mutations, which are the ultimate source of genetic variability • these are mutant bacteria that can digest oil from oil spills

  22. How are mutations caused? • radiation • Chemicals • Can plants be mutants? • Yes

  23. POLYPLOID • Cells that have many sets of chromosomes • drugs prevent chromosomal separation during meiosis • plants can handle this – polyploidy in animals is usually fatal

  24. A polyploid plant is considered a new species • Are any of the fruits and vegetables you eat polyploidy? • bananas and many citrus fruits

  25. Key Concept Questions • What is the purpose of selective breeding?  • Allowing only those organisms with desired characteristics to produce the next generation • Why might breeders try to induce mutations? • To create new combinations of alleles

  26. SECTION 2 Manipulating DNA

  27. Key Concept Questions • How do scientists make changes to DNA?

  28. The code is universal • Since all living organisms… • use the same DNA • use the same code book • read their genes the same way

  29. How are changes made to DNA? • Scientists use their knowledge of the structure of DNA and its chemical properties to study and change DNA molecules. • Different techniques are used to extract DNA from cells, to cut DNA into smaller pieces, to identify the sequence of bases in a DNA molecule, and to make unlimited copies of DNA

  30. GENETIC ENGINEERING • Making changes to the DNA code of a living organism

  31. How do biologists get DNA out of a cell? • cell is opened (cell fractionation) and the DNA is separated from the other cell parts • RESTRICTION ENZYMES • Enzyme used to cut DNA in certain parts of the sequence

  32. Cutting DNA • DNA “scissors” • enzymes that cut DNA • restriction enzymes • used by bacteria to cut up DNA of attacking viruses • cut DNA at specific sites • enzymes look for specific base sequences GTAACG|AATTCACGCTT CATTGCTTAA|GTGCGAA GTAACGAATTCACGCTT CATTGCTTAAGTGCGAA

  33. Many uses of restriction enzymes… • Now that we can cut DNA with restriction enzymes… • we can cut up DNA from different people… or different organisms… and compare it • why? • forensics • medical diagnostics • paternity • evolutionary relationships • and more…

  34. Does it make sense for a biologist to work with a 1 meter long piece of DNA? • No • It is difficult for researchers to study a single copy of a gene so they make more copies • POLYMERASE CHAIN REACTION • Technique that allows molecular biologists to make many copies of DNA

  35. Biologist adds primers to each end of a segment of DNA they want to copy – these small pieces on the end are called primers • DNA polymerase looks for these primers as a place to begin copying • DNA is heated to separate the strands • DNA is then cooled and DNA polymerase hooks on • DNA polymerase makes a copy and the cycle continues until the biologist has the desired amount of DNA • Fig 13-8 p. 325

  36. Comparing cut up DNA • How do we compare DNA fragments? • separate fragments by size • How do we separate DNA fragments? • run it through a gelatin • gel electrophoresis • How does a gel work?

  37. Gel electrophoresis • A method of separating DNA in a gelatin-like material using an electrical field • DNA is negatively charged • when it’s in an electrical field it moves toward the positive side DNA        – + “swimming through Jello”

  38. A mixture of DNA fragments is placed at one end of a porous gel, and an electric voltage is applied to the gel. • When the power is turned on, DNA molecules, which are negatively charged, move toward the positive end of the gel

  39. Gel electrophoresis • DNA moves in an electrical field… • so how does that help you compare DNA fragments? • size of DNA fragment affects how far it travels • small pieces travel farther • large pieces travel slower & lag behind DNA        – + “swimming through Jello”

  40. Gel Electrophoresis DNA &restriction enzyme - longer fragments wells power source gel shorter fragments completed gel +

  41. http://207.207.4.198/pub/flash/4/electrophoresis.swf

  42. How do researchers figure out the sequence of the DNA? • they use fluorescent markers and gel electrophoresis

  43. Running a gel fragments of DNAseparate out based on size Stain DNA • ethidium bromide binds to DNA • fluoresces under UV light cut DNA with restriction enzymes 1 2 3

  44. DNA is placed in a test tube with an enzyme that can make a complimentary strand of DNA • A supply of nucleotide bases – ATGC – is added • A small amount of one of the bases that has been labeled with dye is also added • The enzyme adds the bases along the strand and when it adds a labeled base the strand stops being made

  45. This is repeated with the other three labeled bases • All of the fragments are put into a gel electrophoresis gel • The dye color codes the fragments so biologists know which pieces are which

  46. What can biologists do now that they have separated the DNA into fragments? • RECOMBINANT DNA • DNA molecules produced by combining DNA from different sources, even different organisms • DNA synthesizers – “machines”- enzymes are added to combine sections of DNA together

  47. What role does gel electrophoresis play in the study of DNA? • It enables scientists to separate and analyze DNA fragments, to compare genomes of different individuals and organisms, and to identify a specific gene

  48. Key Concept Questions • How do scientists make changes to DNA? • Through genetic engineering

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