genetic fingerprinting

Question 1

1. What is a variable number tandem repeat (VNTR)?

Answer 1

Non-coding regions of DNA; that contain specific base sequences repeated a certain number of times;

Question 2

2. Explain why VNTRs can be used in genetic fingerprinting.

Answer 2

For every organism the number and length of VNTRs is unique. If DNA is cut with a specific set of restriction enzymes, the number of repeats affects the length between restriction sites. This affects the length of cut fragments, so every organism’s fragment lengths will be different. The probability of two individuals having the same VNTRs is very low (unless they are identical twins.) If the fragments are separated by electrophoresis, a unique pattern will be obtained as the fragments separate out by size.

Question 3

3. What is a restriction site?

Answer 3

The specific sequence of bases (usually palindromic) where a restriction endonuclease will hydrolyse DNA, cutting it into fragments.

Question 4

4. Explain why PCR is used in genetic fingerprinting.

Answer 4

Only small amounts obtained so PCR increases the number of copies of DNA so enough DNA available for genetic fingerprinting;

Question 5

5. Describe how genetic fingerprinting is carried out.

Answer 5

DNA extracted from sample; DNA hydrolysed into segments using restriction endonucleases; leaving variable number tandem repeats (VNTRs) intact; DNA fragments separated using electrophoresis; mixture put into wells on gel and electric current passed through; separate the two strands of DNA; cover with nylon or absorbent paper to absorb DNA; DNA fixed to nylon; labelled probe added which is complementary to the VNTRs; areas with probe identified;

Question 6

6. What is the role of gel electrophoresis in genetic fingerprinting?

Answer 6

Separating fragments of DNA; due to their size; smaller fragments will travel further than larger fragments; The size of DNA fragments can be compared against DNA fragments of known length (DNA ladder).

Question 7

7. Explain why base pairs is a suitable measurement
   for the length of a piece of DNA

Answer 7

DNA made of base pairs; Each base pair is same length;

Question 8

8. Explain why a child’s genetic fingerprint will not be identical to it’s parents?

Answer 8

The child’s DNA will be a combination of both the mother and father’s DNA; Some bands will be the same of the mother and some bands will be the same of the father;

Question 9

9. How can genetic fingerprinting be used to
   investigate the genetic variability within a population?

Answer 9

The more closely two organisms are related, the closer their genetic fingerprints will resemble each other. A population can be tested, if they have similar genetic fingerprints they have little genetic diversity.

Question 10

10. Explain why genetic fingerprinting may be used
    for forensic science, medical diagnosis, animal and plant breeding.

Answer 10

Forensic science – genetic fingerprinting can establish whether a person is likely to have been at a crime scene; Medical diagnosis – genetic fingerprinting can help diagnose diseases such as Huntingdon’s disease; Animal and plant breeding – genetic fingerprinting can be used to prevent inbreeding in captive animals, or identifying individuals with a desirable trait such as disease resistance in plants.

Question 11

11. Why is it useful to run a well containing a selection of fragments of known length alongside the samples?

Answer 11

The size of each band can be determined since the fragment of longest known length will have travelled the least distance and the fragment of smallest length will have travelled the furthest. The size of bands in the patient sample can be determined.