DNA Electrophoresis: BIO 105

information from professor Bobby's lecture notes

DNA Characteristics

• all organisms have the same 4 DNA bases: GCAT

• the order in which the bases are put together are what makes individuals different

• with the exception of identical twins, each individual in the population has a unique sequence of bases

Genetic Fingerprinting (slide 1)

• DNA can be cut with special enzymes termed endonuclease or restriction enzymes

• recognize specific sequences of nucleotides and cut the DNA at these sites

• evolved in bacterial cells as a defense against bacteriophages (bacterial viruses)

Genetic Fingerprinting (slide 2)

• since their discovery in 1962, hundreds of RE have been identified and isolated from bacterial cells

• these RE are extremely specific and work by recognizing short nucleotide sequences in DNA molecules

  • termed Recognition Sequences

  • aka Substrate

• once these sequences are detected, the RE cuts the DNA at this point

Genetic Fingerprinting (slide 3)

For example, EcoR1 cuts at the following recognition sequence:
CTAGATCCGTG|AATTCTATACGGCCTATAG
GATCTAGGCACTTA|AGATATGCCGGATATC

• EcoR1 will cut the DNA every time the above
  recognition sequence is detected

• since everyone has a unique sequence of bases,
  the number of restriction sites will differ from
  person to person

Genetic Fingerprinting (slides 4-6)

ex: Suppose Travis has 4 restriction sites, EcoR1 will cult Joe’s DNA 4 times

• 5 fragments result from the action of EcoR1 when applied to Joe’s DNA

ex: Suppose Taylor’s DNA has 3 restriction sites for EcoR1, EcoR1 will cut Jane’s DNA in three separate places

• 4 DNA segments will result

So, EcoR1 cuts Travis’s DNA into 5 segments and Taylor’s DNA into 4 segments

Genetic Fingerprinting (slide 7)

These fragments can now be separated from one
another using ELECTROPHORESIS
- DNA electrophoresis utilizes an agarose gel and a
voltage current to separate the cut DNA fragments
from one another
- The DNA samples are placed into the agarose gel
(a medium in which the DNA fragments will travel)
and the voltage current separates the fragments

• since every individual has a unique sequence of bases in their DNA, a unique banding pattern will be generated by electrophoresis for each individual

  = genetic fingerprinting