Cutting-Edge DNA Technology & Human Genome Discoveries

1. CHAPTER 12DNA Technology and the Human Genome Modules 12.7 – 12.14

2. OTHER TOOLS OF DNA TECHNOLOGY 12.7 Reverse transcriptase helps make genes for cloning • Reverse transcriptase can be used to make smaller cDNA libraries • These contain only the genes that are transcribed by a particular type of cell

3. CELL NUCLEUS Exon Intron Exon Intron Exon DNA ofeukaryoticgene Transcription 1 RNA transcript RNA splicing(removes introns) 2 mRNA Isolation of mRNAfrom cell and additionof reverse transcriptase;synthesis of DNA strand 3 TEST TUBE Reverse transcriptase Breakdown of RNA 4 cDNA strand Synthesis of secondDNA strand 5 cDNA of gene(no introns) Figure 12.7

4. 12.8 Nucleic acid probes identify clones carrying specific genes • A nucleic acid probe can tag a desired gene in a library Radioactiveprobe (DNA) Mix with single-stranded DNA fromvarious bacterial(or phage) clones Single-strandedDNA Base pairingindicates thegene of interest Figure 12.8A

5. Bacterial colonies containingcloned segments of foreign DNA Radioactive DNA Transfercells tofilter 1 Solutioncontainingprobe Filterpaper • DNA probes can identify a bacterial clone carrying a specific gene Treat cellson filter toseparateDNA strands Add probeto filter ProbeDNA 2 3 Gene ofinterest Single-strandedDNA from cell Hydrogen-bonding Autoradiography 4 Colonies of livingcells containinggene of interest Developed film Compare autoradiographwith master plate 5 Figure 12.8B Master plate

6. 12.9 Connection: DNA microarrays test for the expression of many genes at once • A labeled probe can reveal patterns of gene expression in different kinds of cells • This technique may revolutionize the diagnosis and treatment of cancer cDNA DNA of gene DNAmicroarray,actual size(6,400 genes) Figure 12.9

7. 12.10 Gel electrophoresis sorts DNA molecules by size • Restriction fragments of DNA can be sorted by size Mixture of DNAmolecules ofdifferent sizes Longermolecules Powersource Gel Shortermolecules Glassplates Completed gel Figure 12.10

8. 12.11 Restriction fragment analysis is a powerful method that detects differences in DNA sequences Allele 1 Allele 2 • Scientists can compare DNA sequences of different individuals based on the size of the fragments w Cut z x Cut Cut y y Figure 12.11A DNA from chromosomes

9. 1 2 Longer fragments Shorter fragments Figure 12.11B

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

11. 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 InitialDNAsegment 1 2 4 8 Number of DNA molecules Figure 12.12

12. THE CHALLENGE OF THE HUMAN GENOME 12.13 Most of the human genome does not consist of genes • The 23 chromosomes in the haploid human genome contain about 3 billion nucleotide pairs • This DNA is believed to include about 35,000 genes and a huge amount of noncoding DNA

13. Much of the noncoding DNA consists of repetitive nucleotide sequences • One example includes telomeres at the end of the chromosomes Repeated unit End ofDNAmolecule NUCLEOTIDE SEQUENCE OF A HUMAN TELOMERE Figure 12.13A

14. Barbara McClintock discovered that segments of DNA called transposons can move about within a cell’s genome Figure 12.13B, C

15. 12.14 Connection: The Human Genome Project is unlocking the secrets of our genes • The Human Genome Project involves: • genetic and physical mapping of chromosomes • DNA sequencing • comparison of human genes with those of other species Figure 12.14