7.1 3 DNA profiling Flashcards
DNA profiling
the identification of repeating patterns in the non-coding regions of DNA
Allows us to identify individuals,species ,forensic science and paternity testing
introns
reptitive coding regions between genes
are inherited in the same way as active genes
function of introns
can code for small interfering RNA molecules siRNA that interact with mRNA to prevent the production of certain proteins
within the introns
there are short sequences of DNA that are repeated many times to from micro-satelltes and mini-satellites
same mini or micro appear same position on homologous pairs of chromosomes
what varies is the number of repeates on the maternal and paternal chromosomes
mini-satellite
10-100 bases repeate 50 to several hundred times
micro-satellite
2-6 bases repeated 5 to 100 times
the more closely related two individuals
the more likely there will be similarties in their DNA patterns
FIRST STAGE of DNA profiling
PCR?
strands of DNA from a sample are cut using restriction endonucleases
these enzymes cut the DNA at particular points in intron sequences
recognition sites
different restriction enzymes cut a DNA molecules into fragements at different specific base sequences which are the recogniton sites
using a restriction enzyme
that cut either side of a micro or milli satellite unit leaves the repeated sequences intact giving a mixture of different sized DNA fragments depending on the number of repeated sequences
SECOND STAGE
Gel electrophoresis
fragments need to be separated and identified
process of gel electrophoresis
DNA fragments are placed in wells in agarose gel medium in a buffering solution with a known DNA frament to aid identification
gel contains a dye such as ethidium bromide whcih binds to the DNA fragments in the gel
the dye will fluoresce when placed under UV revealing band of DNA
A visable dye
Also added to DNA samples doesnt bind but moves through gel slightly faster than DNA so current can be turned off before samples run off the end
An electric current
passed through the apparatus and the DNA fragments move towards the positive anode because of the negative charge of the phosphate groups in the DNA backbone
Fragements
Move at different rates according to size due to how easily move through pores in the agrose jelly
THIRD STAGE
Souther blotting
Alkaline buffer solution is added to gel after electrophoresis and a nylon filter or nyloncellulose paper is placed over it
dry absorbent material used to draw solution containing DNA from gel to filter leaving DNA as blots attached to the filter
alkaline solution
also denatures the DNA fragments so the strands separate and the base sequences are exposed
DNA then covalently bound by UV cross linking
After southern blotting process
large quantities of single stranded gene probes are added to the filter and bind to complementary DNA strands in a process known as hybridisation
gene probes
short DNA sequences complementary to specific sequences being sought each probe is labelled to a fluorescent molecule or radioactive isotope
excess probes are washed away and filter placed under a UV light to show up DNA regions
result
A DNA profile is produced as a graph with each peak representing the number of microsatellite repeats in a fragment
forensic science
gene probes are used to pick out short tandem repeats which are micro-satellite regions largely used in DNA identification
paternity testing
Specific micro-satellite markers are used to make the matches
microsatllies must come from mother or father cant be traced to mother or alleged father then isnt the father
