12.10 Gel electrophoresis sorts DNA molecules by size Restriction fragments of DNA can be sorted by size Mixture of DNA molecules of different sizes Longer molecules Power source Gel Shorter molecules Glass plates Completed gel Figure 12.10

12.11 Restriction fragment analysis is a powerful method that detects differences in DNA sequences Scientists can compare DNA sequences of different individuals based on the size of the fragments Allele 1 Allele 2 w Cut z x Cut Cut y y Figure 12.11A DNA from chromosomes

1 2 Longer fragments Shorter fragments Figure 12.11B

Radioactive probes are also used to make comparisons 1 Restriction fragment preparation Restriction fragments 2 Gel electrophoresis Filter paper 3 Blotting 4 Radioactive probe Radioactive, single- stranded DNA (probe) Probe 5 Detection of radioactivity (autoradiography) Film Figure 12.11C

12.12 The PCR method is used to amplify DNA sequences The polymerase chain reaction (PCR) can quickly clone a small sample of DNA in a test tube Initial DNA segment 1 2 4 8 Number of DNA molecules Figure 12.12

12.15 Connection: DNA technology is used in courts of law OTHER APPLICATIONS OF DNA TECHNOLOGY 12.15 Connection: DNA technology is used in courts of law DNA fingerprinting can help solve crimes Defendant’s blood Blood from defendant’s clothes Victim’s blood Figure 12.15A, B

12.16 Connection: Recombinant cells and organisms can mass-produce gene products Recombinant cells and organisms are used to manufacture useful proteins Table 12.16

These sheep carry a gene for a human blood protein that is a potential treatment for cystic fibrosis Figure 12.16

12.17 Connection: DNA technology is changing the pharmaceutical industry and medicine Hormones, cancer-fighting drugs, and new vaccines are being produced using DNA technology This lab equipment is used to produce a vaccine against hepatitis B Figure 12.17

New genetic varieties of animals and plants are being produced 12.18 Connection: Genetically modified organisms are transforming agriculture New genetic varieties of animals and plants are being produced A plant with a new trait can be created using the Ti plasmid

Agrobacterium tumefaciens DNA containing gene for desired trait Plant cell 1 2 3 Ti plasmid Recombinant Ti plasmid Insertion of gene into plasmid using restriction enzyme and DNA ligase Introduction into plant cells in culture Regeneration of plant T DNA T DNA carrying new gene within plant chromosome Plant with new trait Restriction site Figure 12.18A

“Golden rice” has been genetically modified to contain beta-carotene This rice could help prevent vitamin A deficiency Figure 12.18B

Cloned gene (normal allele) 12.19 Connection: Gene therapy may someday help treat a variety of diseases Cloned gene (normal allele) Techniques for manipulating DNA have potential for treating disease by altering an afflicted individual’s genes Progress is slow, however There are also ethical questions related to gene therapy 1 Insert normal gene into virus Viral nucleic acid Retrovirus 2 Infect bone marrow cell with virus 3 Viral DNA inserts into chromosome Bone marrow cell from patient Bone marrow 4 Inject cells into patient Figure 12.19

RISKS AND ETHICAL QUESTIONS 12.20 Connection: Could GM organisms harm human health or the environment? Genetic engineering involves some risks Possible ecological damage from pollen transfer between GM and wild crops Pollen from a transgenic variety of corn that contains a pesticide may stunt or kill monarch caterpillars Figure 12.20A, B

12.21 Connection: DNA technology raises important ethical questions Our new genetic knowledge will affect our lives in many ways The deciphering of the human genome, in particular, raises profound ethical issues Many scientists have counseled that we must use the information wisely Figure 12.21A-C