Genetic fingerprinting

Genomes

  • Genome = all the genetic material in an organism

  • Not all of an organisms genome codes for proteins

  • contain non-coding variable number tandem repeats (VNTRs) — base sequences that don’t code for proteins and repeat next to each other over and over

  • The number of times these sequences are repeated differs from person to person, so the length of sequences in nucleotides differs too

  • The repeated sequences occur in lots of places in the genome

  • The number of times a sequence is repeated at different places in their genome can be compared between individuals (this is called genetic fingerprinting)

  • The probability of two individuals having the same genetic fingerprint is very low because the chance of two individuals having the same number of VNTRs at each place they’re found in DNA is very low

Genetic fingerprinting - making

  1. a sample of DNA is obtained (from blood, saliva etc)

  2. PCR is used to make many copies of the area of DNA That contain the VNTRs - primers are used that bind to either side of these repeats so the whole repeat is amplified

  3. You end up with DNA fragments where the length in nucleotides corresponds to the number of repeats the person has at each specific position

  4. A fluorescent tag is added to all the DNA fragments so they can be viewed under a UV light

  5. The DNA fragments undergo electrophoresis

  6. The DNA fragments are viewed as bands under UV light, this is the genetic fingerprint

  7. Two fingerprints can be compared, if they have bands at the same location on the gel it means they have the same number of nucleotides and the same number of VNTRs at that place, so they are a match

Electrophoresis

— used to separate DNA fragments to make genetic fingerprint —

  • DNA mixture is placed into a well in a slab of gel and covered in a buffer solution that conducts electricity

  • An electrical current is passed through the gel (DNA fragments are negatively charged so they move towards positive electrode)

  • Small DNA fragments more faster and travel further through the gel, so the DNA fragments separate according to size

(Finish pg 220)