Genetic Fingerprinting

Question 1

What are variable number tandem repeats?

Answer 1

Non-coding repeat sequences found in between genes

Question 2

How do VNTRs compare in species?

Answer 2

• share the same VNTR sequences at the same loci but the number of repeats varies between organisms

Question 3

How are DNA fragments produced of varying sizes?

Answer 3

• VNTRs cut out using restriction endonuclease
• cuts at specific base sequences found on both ends of the VNTR sequence
• so DNA fragments produced vary in size

Question 4

How does gel electrophoresis separate DNA fragments?

Answer 4

• using electrical current
• separate according to their size, smaller fragments travel further through the gel
• loaded into the well at the negative end and move towards the positive end

Question 5

What are DNA ladders?

Answer 5

• samples of DNA of known, different lengths are loaded into one of the wells
• DNA is measured in base pairs as the distance between each base pair remains the same
• the DNA ladder is used to help determine the size of an unknown DNA sample

Question 6

How are the DNA fragments made visible during gel electrophoresis?

Answer 6

• nylon membrane placed over the gel
• DNA fragments stick to the membrane
• radioactive DNA probes are added to the membrane and will hybridise with complementary base sequences on the DNA fragments
• membrane is washed to remove unbound DNA probes and X-ray is used to identify where the DNA probes have bound

Question 7

What is the overall process of genetic fingerprinting?

Answer 7

1. DNA is extracted and amplified by PCR
2. Restriction endonuclease cut the DNA at specific VNTR sequences
3. DNA fragments separated by gel electrophoresis by size and transferred to nylon membrane
4. DNA probes hybridise with complementary VNTR sequences forming hydrogen bonds
5. Excess probes are washed away and the membrane with radioactively labelled VNTR fragments are placed into Xray film, revealing where the probes have attached

Question 8

Why are genetic fingerprints described as unique?

Answer 8

The probability of two people having the same band pattern is very low

Question 9

What are some uses of genetic fingerprinting?

Answer 9

• forensic science
• paternity cases
• medical diagnosis
• animal and plant breeding/ relationships to prevent inbreeding
• determining genetic variation