Component 2.7 - Genetic Techniques

Question 1

Explain what gives individuals a unique DNA profile and how this is used to make a DNA profile in the UK

Answer 1

1) An individuals DNA profile is different to that of another’s
2) Exons code for DNA and are similar because we are the same species
3) Introns have sequences called Short Tandem Repeats (blocks of repeated nucleotides) and the number of repeats is different in each individual
4) A number of STRs will be used to make a DNA profile

Question 2

What 2 processes does DNA sequencing rely on?

Answer 2

1) The polymerase chain reaction (to amplify small sections of DNA rapidly)
2) Gel electrophoresis

Question 3

What happens in the first step of the polymerase chain reaction?

Answer 3

1) Target DNA heated to 95 degrees so it splits

Question 4

What happens in the second step of the polymerase chain reaction?

Answer 4

2) Solution cooled to 55 degrees and primers (which are complementary to the start of the sequence) attach to complementary bases on the single strand of DNA

Question 5

What happens in the third step of the polymerase chain reaction?

Answer 5

3) Solution heated to 70 degrees - taq polymerase catalyses the synthesis of a complementary strand by adding complementary nucleotides and forming sugar-phosphate backbone (extension)

Question 6

What happens to the DNA before it goes in the thermocycler?

Answer 6

1) The DNA solution is dissolved in a buffer
2) It is mixed with taq polymerase
3) It is mixed with nucleotides and short single stranded pieces of DNA complementary to the start of the DNA strand

Question 7

Limitations of the polymerase chain reaction

Answer 7

• Any DNA that enters the system can get amplified

- Taq polymerase cannot correct itself like DNA polymerase

Question 8

What happens to the DNA before it undergoes gel electrophoresis?

Answer 8

• The DNA is extracted and cut to make DNA fragments using restriction endonucleases
• DNA are loaded in wells at one end of the agarose

Question 9

How are DNA fragments separated by gel electrophoresis?

Answer 9

1) Voltage is applied across the gel
2) Phosphate groups in the DNA backbone are negatively charged and attracted to positive electrode
3) Shorter fragments travel further than larger fragments as it easier for them to travel through pores in the gel

Question 10

Uses of DNA profiling?

Answer 10

Siblings - if they have similar banding they can prove to be biological siblings

Paternity - bands on the DNA profile of the alleged father line up with the DNA profile of the child where the mother does not

Monozygotic twins - have identical banding patten

Dizygotic twins - don’t have an identical banding pattern

Question 11

What are the pros of DNA profiling?

Answer 11

• Can be used on samples too small for blood testing
• Reversed wrongful convictions
• Can use urine/mouth swabs instead of blood (non invasive)

Question 12

What are the cons of DNA profiling?

Answer 12

• Some people think that a request for DNA is a violation of privacy
• Computer databases with DNA profiles could get hacked
• Limited access (e.g no health insurers)
• DNA profiling may produce wrongful convictions e.g performed incorrectly, people may not be trustworthy

Question 13

How can fragment size be estimated?

Answer 13

By running a DNA ladder alongside as it contains fragments of known size