Forensics

Question 1

Explain the role of DNA primers in the production of the amplified 345bp sequence. (2)

Answer 1

• primers have a specific base sequence
  which bind to complimentary bases of the amplified DNA
• therefore a site for DNA polymerase to bind

Question 2

Explain why the amplified DNA fragments for the G20210A allele and the wild type allele are different. (3)

Answer 2

• base sequence of the alleles are different
• therefore restriction enzyme cuts at specific DNA base seq which is found specifically on G20210A
• therefore a shorter fragment produced

Question 3

Devise an investigation to determine optimum number of cycles for polymerase chain reaction used to amplify DNA for this test. (4)

Answer 3

• heat mixture to around 95° to break hydrogen bonds b/w DNA strands
• mixture cooled to 60° so primer can anneal
• use gel electrophoresis to determine quantity of DNA produced

Question 4

Comment on effect of adding cow dung to composting coffee husks. (3)

Answer 4

• start of composting: % of organic carbon is lower, % of nitrogen is higher
• adding cow dung does not effect organic carbon
• but causes slight change to nitrogen %

Question 5

Describe how this study could be carried out. (pigs)

Answer 5

• control: size and breed of pigs
  & temp
• record types of different insects which colonise body every hour

Question 6

Explain how results of this study (pigs) could be used to help establish time of death of a human. (3)

Answer 6

• by looking at life cycle of organism that is present and recording the types
• compare the results with the results from the time of death of pigs

Question 7

Describe how DNA profiling could be carried out to show that these snakes are diff species. (4)

Answer 7

• DNA samples from diff types of grass snakes taken and amplified using PCR
• DNA fragments separated by length
• larger fragments slower than shorter
• UV light reveals the different bands which can be compared to show that they are different species

Question 8

Describe how one PCR cycle would increase DNA quantity. (3)

Answer 8

• heat to 95: separates DNA strands
• annealing at 60

^ doubles quant. of DNA

Question 9

Explain how microorganisms in soil break down stems. (3)

Answer 9

• stem contains starch
• enzymes secreted by microorganism

^ break down glycosidic bonds

Question 10

Explain effect of ambient temp on decomposition rate. (3)

Answer 10

• increased temp = increased decomposition rate

& increased enzyme activity

& increased growth rate of decomposers

Question 11

Explain how gel electrophoresis can be used to find out if the DNA is from a black panther. (5)

Answer 11

• current applied across gel
• use DNA stain
• also use DNA of black panther
• compare bands
• match indicated that black panther is present

Question 12

Devise a procedure to compare amplified DNA from these two human types. (4)

Answer 12

• restriction enzymes used to cut DNA into fragments
• DNA samples loaded into agarose gel
• electric current passed through gel
• position of bands produced can be compared

Question 13

Describe the role of decomposers in the carbon cycle. (2)

Answer 13

• break down organic materials
• respire, releasing CO2 into atmosphere

Question 14

Describe the changes that occur inside the body in the first week after death. (3)

Answer 14

• body temp. falls
• rigor mortis
• breakdown of tissues by enzymes