dna sequencing
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DNA SequencingLauren Schroer
What is DNA Sequencing?
• DNA Sequencing is a technique used to determine the order of nucleotides in a gene.
Steps in DNA Sequencing
• DNA Sequencing consists of four main steps:– Polymerase Chain Reaction (PCR)– Sequencing Reaction– Gel Electrophoresis – Computer Scanning
Step 1: PCR
• Chromosomes (50-250 million bases long) are multiplied and broken up into shorter fragments.
Step 2: Sequencing Reaction
• Reaction is done with dideoxyribonucleotides (just like regular DNA without 3’ hydroxyl group), which when added to the end make it impossible for the DNA to elongate.
• Restriction enzymes cut at these dideoxyribonucleotides. (Ex: Dideoxy-T)
• The place on the strand that is cut is random each time so eventually the cut strands will end with every individual T (or A,G, or C), in the sequence.
Step 3: Gel Electrophoresis
• The fragments are set in and then separated by Gel Electrophoresis.
• Flourescent dyes are used to identify the end nucleotide (if it is an A, T, G, or C).
Step 4: Computer Scanning
• Computers ‘read’ the sequence from the gel and interpret the colors and print a sequence of nucleotides across the top.
Limitations
• Currently only 500-900 bases can be sequenced with each read.
• Less expensive methods are less accurate.
Ethical Concerns
• Some people believe that a person’s DNA sequence is their business, and their business only, and if DNA sequencing becomes too common it could be abused.
Sources• "How Do We Sequence DNA?" How Do We Sequence DNA? Web. 23
May 2012.<http://seqcore.brcf.med.umich.edu/doc/educ/dnapr/sequencing.html>.
• "Tiny Reader Makes Fast, Cheap DNA Sequencing Feasible." ScienceDaily. ScienceDaily, 26 Mar. 2012. Web. 23 May 2012. <http://www.sciencedaily.com/releases/2012/03/120326160651.htm>.
• "DNA Sequencing, Without the Fuss." ScienceNOW. Web. 23 May 2012. <http://news.sciencemag.org/sciencenow/2012/03/dna-
sequencing-without-the- fuss.html>.
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