CSB349 - Lecture 2.doc

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Cell and Systems Biology
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Alan Moses

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CSB349 Lecture 2 - Moses What is in the human genome? Its very large… ~3 gigabases 99% of the euchromatin and several million bps still not sequenced Most was repetitive DNA  very hard to sequence! The heterochromatin  telomeres, centromeres Most that was sequences was also repetitive elements  transposons (~45%) Only 1.5% of genome is actual genes Types of repetitive DNA Tandem: the repeats are right beside each other Interspersed: repeats are not near each other, can be anywhere in the genome Tandem: Satellite: huge sequences, centromere (heterochromatic) important for chromosomes! Minisatellite: heterochromatic, TELOMERES, smaller sequences that satellites Microsatellite: very small in basepairs and repeats, incredibly variable between individuals, used in DNA fingerprinting in crime scenes, etc. Interspersed: Transposons: DNA jumping genes, have a transposase gene MITES: don’t have a transposase gene SINES: related to retroviruses LINES: Measuring copy number with PCR (for microsatellites, small repeats) Use a primer pair (with known lengths) on either side of the repeated element. Primer is the non-repetitive sequence flanking the repeated microsatellite. Do the PCR and then run a gel. The DNA will show up as a bunch of bands but approximately the same sizes. WHY? During replication the tandem repeats undergo replication slippage, where the polymerase either hikes up or down a little bit and either doesn’t copy some of the bps or adds additional base pairs to the the repeated DNA. This is why you may see multiple bands together on the gel with slightly diff sizes. This is also how tandem repeats are generated. Slippage can result in disease if the repeat numbers rise a lot: e.g. Huntington’s Longer repeats are caused by (problems in recombination or DNA repair): -
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