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Anne Houtman • Megan Scudellari • Cindy Malone
Biology Now SECOND EDITION Chapter 9 What Genes Are © 2018 W. W. Norton & Company, Inc.
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Pig face and snout close up Mike Kemp/Rubberball/Getty Images.
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Figure 9.1 Experimental pig-to-baboon lung transplant A lung from a pig engineered by CRISPR to prevent rejection is tested for safety and efficacy in primates by being transplanted into a baboon. Photo credit: Chris Maddaloni/Nature. from Reardon, S., New life for pig-to-human transplants: Gene-editing technologies have breathed life into the languishing field of xenotransplantation. Nature 527, (12 November 2015) doi: /527152a.
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Photo courtesy of Dr. Marc Guell.
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Rick Friedman/Corbis via Getty Images.
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Figure 9.2 Pig and human organs are remarkably similar in size
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Figure 9.2 Pig and human organs are remarkably similar in size
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Figure 9.3 The DNA double helix and its building blocks A molecule of DNA consists of two complementary strands of nucleotides that are twisted into a spiral around an imaginary axis, rather like the winding of a spiral staircase.
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Figure 9.3 The DNA double helix and its building blocks A molecule of DNA consists of two complementary strands of nucleotides that are twisted into a spiral around an imaginary axis, rather like the winding of a spiral staircase.
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Figure 9.3 The DNA double helix and its building blocks A molecule of DNA consists of two complementary strands of nucleotides that are twisted into a spiral around an imaginary axis, rather like the winding of a spiral staircase.
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Figure 9.3 The DNA double helix and its building blocks A molecule of DNA consists of two complementary strands of nucleotides that are twisted into a spiral around an imaginary axis, rather like the winding of a spiral staircase.
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Figure 9.6 Genome editing with CRISPR-Cas9, an efficient and cost-effective tool
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Figure 9.6 Genome editing with CRISPR-Cas9, an efficient and cost-effective tool
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Figure 9.7 Chromosomes are meticulously organized DNA-protein complexes The DNA double helix is continuously coiled and packaged around proteins until it is compacted into a chromosome.
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Figure 9.7 Chromosomes are meticulously organized DNA-protein complexes The DNA double helix is continuously coiled and packaged around proteins until it is compacted into a chromosome.
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Figure 9.8 DNA replication is semiconservative In this overview of DNA replication, the template DNA strands are blue, and the newly synthesized strands are magenta.
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Figure 9.8 DNA replication is semiconservative In this overview of DNA replication, the template DNA strands are blue, and the newly synthesized strands are magenta.
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Figure 9.9 PCR can amplify small amounts of DNA more than a millionfold Short primers consisting of synthetic DNA segments are mixed in a test tube with a sample of the target DNA, the enzyme DNA polymerase, and all four nucleotides (A, C, G, and T). The primers form base pairs with the two ends of a gene of interest. A machine then processes the mixture and doubles the number of double-stranded versions of the template sequence. The doubling process can be repeated many times (only three cycles are shown here).
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Figure 9.9 PCR can amplify small amounts of DNA more than a millionfold Short primers consisting of synthetic DNA segments are mixed in a test tube with a sample of the target DNA, the enzyme DNA polymerase, and all four nucleotides (A, C, G, and T). The primers form base pairs with the two ends of a gene of interest. A machine then processes the mixture and doubles the number of double-stranded versions of the template sequence. The doubling process can be repeated many times (only three cycles are shown here).
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Figure 9.10 Repair proteins fix DNA damage Large complexes of DNA repair proteins work together to fix damaged DNA.
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Figure 9.10 Repair proteins fix DNA damage Large complexes of DNA repair proteins work together to fix damaged DNA.
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Figure 9.11 A point mutation in the hemoglobin gene leads to sickle-cell disease In people with the genetic disorder sickle-cell disease, a single base in the gene that makes hemoglobin, an important protein involved in oxygen transport in red blood cells, is altered. The red blood cells of people with sickle-cell disease become curved and distorted under low-oxygen conditions and can clog blood vessels, leading to serious effects, including heart and kidney failure. Left Normal Blood Cells Dr. Tony Brain/SPL/Science Source. Right Sickle Blood Cells Meckes Ottawa/Science Source.
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Figure 9.12 Human organs could grow up in pigs Growing a human organ (here, a kidney) in pigs modified by CRISPR to lack that organ could help meet transplant needs.
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Figure 9.12 Human organs could grow up in pigs Growing a human organ (here, a kidney) in pigs modified by CRISPR to lack that organ could help meet transplant needs.
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PubMed search results for C R I S P R by year
Search results article count 2002 1 2003 2004 2005 5 2006 6 2007 12 2008 21 2009 32 2010 45 2011 79 2012 126 2013 282 2014 607 2015 1,258 2016 2,143 C R I S P R timeline by year 1978 C R I S P R repeats are first observed in bacterial genomes. Their significance is not yet known. 2002 The term C R I S P R is coined by researchers in Spain and the Netherlands. 2006 Researchers propose that C R I S P R functions in nature as part of a bacterial adaptive immune system. 2011 The final necessary place for the genome editing system is identified: a second small RNA needed to guide Cas9 to its targets. 2013 The C R I S P R-Cas9 system is used to edit targeted genes in both human and mouse cells and later plant cells. 2015 In China, scientists use C R I S P R-Cas9 to edit preimplantation human embryos, repairing a mutated gene that would cause a blood disorder. Subsequently, an international ban prohibits the use of genome editing to make changes to the human genome. 2016 The first human trail to use C R I S P R genome from the national Institute of Health, in a cancer therapy trial to edit a patient's own immune system cells.
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