DNA Profiling Summary (A-Level 2nd Year)

DNA Profiling/Fingerprinting


Principles:
 Uses non-coding DNA (doesn’t code for proteins) because all humans have SAME
GENES (Coding DNA)
 Alleles = genes (base sequence) that have mutated (changed) bring about variation.
 Uses repetitive sequences in non-coding DNA which vary in number of repeat
sequences (length of DNA fragment) in each individual
 GEL ELECTROPHORESIS separates these DNA fragments by length.
 Each individual had unique DNA barcode (except identical twins)




 Each person has non-coding DNA in known LOCI that contains repeated DNA
sequence
 Number of repeats of sequence varies between each person for each locus
*CAGTCACAGTCACAGTCA* = variable number tandem repeats (VNTR’s)
 Short repeat *CATCATCAT* = Short Tandem Repeats (STR’s)
 Number of repeats in sequence (VNTR’s/STR’s) makes length different
 Each person carries 2 alleles of each of these repeat sequences because they get 1
allele from mum + 1 from dad. (if present on locus of 1 chromosome; will be at the
same locus on homologous chromosome.




 VNTR/STR’s cut using restriction endonucleases
 Enzymes - Cut DNA at specific base sequences
 Mixture of VNTR/STRs can be separated by length + charge by gel electrophoresis
(chromatography)
 DNA = Acid so gives away H+ and leaves DNA molecule to be negative
 Use electricity to separate DNA segments of different lengths, those negative strands
go to positive electrode
 Results in DNA fingerprint
 Shorter DNA fragments = move faster than long ones




EXAM SPEAK METHOD
 Uses VNTR/STRs – regions of non-coding with variable base sequence repeats