DNA Profiling
•Not quite as unique as fingerprints
•Only people with identical genomes will
have identical DNA profiles (identical
twins or clones)
•Our DNA is full of polymorphic loci – specific locations
on homologous chromosomes that vary in length
between individuals.
•Loci are given specific “addresses” or names, i.e. PV92
600 bp
300 bp
Notice the 300 extra base pairs in the maternal copy
of this individual’s chromosome 16.
The “extra” bases at Polymorphic Loci
are from:
• SHORT TANDEM REPEATS (STRs)
• VARIABLE NUMBER of TANDEM
REPEATS (VNTRs)
• TRANSPOSABLE ELEMENTS
(TRANSPOSONS)
Short Tandem Repeats (STRs)
• Short DNA sequences (2 -10 base pairs) that
repeat several time
• Currently over 10,000 published STR sequences in
the human genome
•STR analysis has
become the prevalent
method used by the FBI
•The FBI uses 13 different polymorphic loci when creating
a DNA profile
•(PV92 is not one of them)
Variable Number of Tandem Repeats (VNTRs)
• Short DNA sequences (14 to 100 base pairs)
repeated 4 -40 times per occurrence
• Scattered on many chromosomes
•We’ll use PCR to amplify the DS180 locus on
chromosome 1 that contains a 16 bp sequence that
repeats between 14 and 40 times (depending on the
person).
Click me and select
“human DNA
polymorphisms”
Transposons (Jumping Genes)
Segments of DNA that can move from one place
to another in the genome
Alu – a transposon that is approximately 300 bp
in length, found all over the human genome.
This locus either has or does not have the Alu insertion, and
you can be either homozygous or heterozygous for this
insertion.
•Student 1 has no Alu insert on either chromosome 16 =
homozygous
•Student 2 has no Alu insert on 1 copy of chromosome 16,
and does have the Alu insert on the other copy of
chromosome 16 = heterozygous
•Student 3 has the Alu insert on both copies of chromosome
16 = homozygous