genetic fingerprinting

Question 1

genetic fingerprint is a?

Answer 1

persons dna profile

Question 2

what two techniques does a genetic fingerprint rely on?

Answer 2

• the polymerase chain reaction to make large numbers of copies of DNA fragments

-gel electrophoresis, to separate the DNA fragments based on their size

Question 3

STR’s

Answer 3

part of DNA used to make a genetic fingerprint

Question 4

PCR

Answer 4

Polymerase Chain RxN

-technique used to amplify DNA (where only small samples are available in order to make enough for analysis)

Question 5

stages of PCR

Answer 5

1. The DNA is heated to 95°C to separate the two strands of the DNA molecule (hydrogen bonds broken)
2. The temperature is cooled to 50-60°C to allow primers to anneal (join) to the DNA.
3. The temperature is raised to 70°C and a thermally stable Taq DNA polymerase attaches new nucleotides to their complementary base pairs on each strand. It joins them one at a time by catalysing formation of phosphodiester bonds between the sugar and phosphate molecules, making the backbone. This is termed the extension phase.
4. The temperature in the thermocycler is raised to 95°C and the cycle is repeated. After about 40 cycles there will be over a billion copies of the DNA.

Question 6

what happens when there is more DNA than primers, enzymes and free nucleotides?

Answer 6

the slower the reaction because the single stranded DNA strands are more likely to pair with each other rather than a primer, limiting how many cycles can be done.

Question 7

when is PCR most effective?

Answer 7

PCR is most effective on DNA sequences between 1000 and 3000 bases long.

Question 8

gel electrophoresis

Answer 8

This technique separates DNA fragments by length.

(Beforehand the DNA needs to ‘cut’ into fragments. The enzymes used are restriction endonucleases which hydrolyse phosphodiester bonds at specific base sequences on the DNA. There are a number of different types of restriction endonucleases. This is the basis of the bands of a genetic fingerprint.)

Question 9

where is gel electrophoresis used?

Answer 9

Gel electrophoresis is used in Sanger sequencing as well as genetic fingerprinting.

Question 10

what is a primer??

Answer 10

a strand of DNA about 10 nucleotides long that base pairs with the end of another longer strand, making a double stranded section, to which DNA polymerase may attach prior to replication.

Question 11

what is important about dan fragments used in PCR??

Answer 11

that they are not contaminated with any other biological material as the contaminants may contain DNA, which would also be copied.

Question 12

limitations of using PCR - SUMMARY

Answer 12

-error state
-its limit on suitable fragment size
-the presence of inhibitors and contaminants
-biochemical limits to the process

Question 13

why is PCR used with forensic scientists?

Answer 13

often used when producing a genetic fingerprint, to increase the quantity of DNA because the sample obtained at a crime scene may be very small