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

12.7 Reverse transcriptase helps make genes for cloning 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

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

12.8 Nucleic acid probes identify clones carrying specific genes A nucleic acid probe can tag a desired gene in a library Radioactive probe (DNA) Mix with single- stranded DNA from various bacterial (or phage) clones Single-stranded DNA Base pairing indicates the gene of interest Figure 12.8A

DNA probes can identify a bacterial clone carrying a specific gene Bacterial colonies containing cloned segments of foreign DNA Radioactive DNA 1 Transfer cells to filter Solution containing probe Filter paper 2 Treat cells on filter to separate DNA strands 3 Add probe to filter Probe DNA Gene of interest Single-stranded DNA from cell Hydrogen-bonding 4 Autoradiography Colonies of living cells containing gene of interest Developed film 5 Compare autoradiograph with master plate Figure 12.8B Master plate

This technique may revolutionize the diagnosis and treatment of cancer 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 DNA microarray, actual size (6,400 genes) Figure 12.9

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

12.13 Most of the human genome does not consist of genes 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

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

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

The Human Genome Project involves: 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