mcb104 handout week 3 - M CB 104 discussion sections 101 &...

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MCB 104 discussion sections 101 & 106 MOLECULAR MARKERS In humans, there are not many mendelian traits with obvious physical phenotypes, but there are many ‘molecular phenotypes’ hidden in the DNA sequence, and these can be used as molecular markers. Molecular markers results from slight variation in the DNA sequence between individuals, and follow Mendel’s laws, as do genes. One kind of variation is a S ingle N ucleotide P olymorphism (SNP), which is a single base pair mutation or substitution. Another kind is of variation is in the number of tandem repeats in microsatellite DNA, or simple sequence repeats. These types of variation do not usually result in a phenotypic difference, but can be differentiated through molecular techniques such as PCR or restriction enzyme digestion. Restriction Fragment Length Polymorphisms (RFLPs) are SNPs that result in creating or abolishing a restriction enzyme site. DNA at a particular site of interest is cut with a restriction enzyme. The restriction enzyme will recognize and cut one allele (the one that contains the DNA sequence recognized by the restriction enzyme) but not another allele (which has a mutation in the DNA sequence and is no longer recognized by the restriction enzyme). The DNA is then analyzed by Southern blot: first is ran out on agarose gel (to separate the DNA fragments based on their size) and then it is probed with a small piece of labeled (usually radioactive or fluorescent) DNA that is complementary to the DNA of interest. This technique allows to visualize the DNA and determine which alleles of
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This note was uploaded on 01/28/2010 for the course MCB 104 taught by Professor Urnov during the Fall '09 term at University of California, Berkeley.

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mcb104 handout week 3 - M CB 104 discussion sections 101 &...

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