Text of 4.4 Biotechnology - DNA Profiling (by Daniel)
DNA Profiling C_Daniel Yoon
What is DNA Profiling?A technique used to identify individual
by encrypting setsof numbers that reflect a persons DNA makeup.
(Oftenused in parental testing and criminal investigation)
Assessment Statement related to DNA Profiling4.4.3 State that
gel electrophoresis of DNA is used inDNA profiling.4.4.4 Describe
the application of DNA profiling todetermine paternity and also in
forensicinvestigations.4.4.5 Analyse DNA profiles to draw
conclusions aboutpaternity or forensic investigations.
How does gel electrophoresis work?Gel electrophoresis is used
to separate DNA (or othermolecules) by their size and charge. The
DNA fragmentsmove in an electric field. The negatively charged DNA
allmoves towards the positive electrode. Small pieces movefarther
than large pieces.
Procedure of DNA Profiling1. DNA samples are taken and
amplified with PCR2. Restriction enzymes cut DNA into fragments at
specific base sequencesin each sample3. a fluorenscent marker
blinds to a triplet in the DNA fragments, so thatresults can be
seen4. Samples are added to a gel electrpphoresis chamber. Electric
current ispassed through, pushing the fragments along5. Heavier
fragments stay closer to the origin and smaller fragments
gofurther6. a banding pattern shows up for each DNA sample and can
What is PCR (polymerase chain reaction) used for?-copy and
amplify tiny quantities of DNA. Very useful ifyou only have a small
sample of DNA (like from a bloodsample from a patient or a crime
scene) and you need lotsof DNA to do DNA profiling.
Which electrode (positive ornegative) will DNA travel towards
in gel electrophoresis? Why?positive electrode; DNA is negatively
charged (think of allof those phosphate groups!). Note that if the
electrodes arenot labelled in a gel
4.4.5 Analyse DNA profiles todraw conclusions about paternity
or forensic investigations.
From Senior biology BookMicrosatellites(short tandem repeats):
repeatingsequences(2-6 base pairs)Because noncoding nucleotide
sequences repeatthroughout the genome, the finding of
repeatingsequences(DNA profiling) is possible.
4.4.4 Describe the application of DNA profiling to determine
paternity and also in forensic investigations.Organisms have short
sequences of bases which are repeated many times.These are called
satellite DNA. These repeated sequences vary in lengthfrom person
to person. The DNA is copied using PCRand then cut up intosmall
fragments using restriction enzymes. Gel electrophoresis
separatesfragmented pieces of DNA according to their size and
charge. This gives apattern of bands on a gel which is unlikely to
be the same for twoindividuals. This is called DNA profiling. DNA
profiling can be used todetermine paternity and also in forensic
investigations to get evidence tobe used in a court case for