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CSB349H1 Lecture Notes - Dna Profiling, Transposase, Minisatellite

Cell and Systems Biology
Course Code
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
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.
Transposons: DNA jumping genes, have a transposase gene
MITES: don’t have a transposase gene
SINES: related to retroviruses
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):
- unequal crossing over (replicated chromosomes)
- unequal sister chromatid exchange (single chromosome)
- during DNA replication fork formation
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