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Using genomes and gene technologies homework 
Name                                    Mark:  /24
Question/Skill I struggled with | Plan of action to improve
Q1. One way to detect and measure accurately the amount of RNA in a tissue sample is by RT-PCR (reverse transcriptase-polymerase chain reaction). RT-PCR uses a reaction mixture containing:
•   the sample for testing
•   reverse transcriptase
•   DNA nucleotides
•   primers
•   DNA polymerase
•   fluorescent dye.
The principle behind this method is shown in Figure 1.
 
(a)     Explain the role of reverse transcriptase in RT-PCR.
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(b)     Explain the role of DNA polymerase in RT-PCR.
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(c)     Any DNA in the sample is hydrolysed by enzymes before the sample is added to the reaction mixture.
Explain why.
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(d)     Figure 2 shows the results from using RT-PCR to detect RNA in two different samples, A and B.

A quantitative comparison can be made of the amount of RNA in samples A and B. This involves determining the number of cycles required to reach 50% maximum concentration of DNA (C).
The amount of RNA in a sample can be measured as: 
Use this information to calculate the ratio for RNA content in sample A : RNA content in sample B.
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(e)     Suggest one reason why DNA replication stops in the polymerase chain reaction.
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(f)     Scientists have used the RT-PCR method to detect the presence of different RNA viruses in patients suffering from respiratory diseases.
The scientists produced a variety of primers for this procedure.
Explain why.
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(Total 9 marks)

Q2.           Read the following passage.
The giant panda is one of the rarest animals in the world and is considered to be on the brink of extinction in the wild. Giant pandas have been kept and bred in zoos with the hope that they could be released into the wild. One worry is that small populations, like those in zoos, reduce the genetic variation needed to allow the species to
5        adapt to changing conditions. Unfortunately, pandas find it difficult to reproduce in captivity. Fertilisation of the females is guaranteed only by insemination with semen from several males. With so many potential fathers, the true paternity of the cubs is not clear. It is important to identify the fathers to maintain genetic variation.
10      Panda faeces can be collected in the wild. The faeces contain DNA from the panda, from the bamboo on which they feed and from bacteria. The DNA is subjected to the polymerase chain reaction (PCR). The primers used attach only to the panda DNA. The resulting DNA is subjected to genetic fingerprinting. This can help us to count the number of individuals in the wild because it allows us to identify individual pandas.
Use information in the passage and your own biological knowledge to answer the questions.
(a)     Describe how genetic fingerprinting may be carried out on a sample of panda DNA.
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(b)     (i)      Explain how genetic fingerprinting allows scientists to identify the father of a particular panda cub.
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(ii)     When pandas are bred in zoos, it is important to ensure only unrelated pandas breed. Suggest how genetic fingerprints might be used to do this.
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(c)     (i)      Suggest why panda DNA is found in faeces. (line 10)
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(ii)     Explain why the PCR is carried out on the DNA from the faeces. (line 12)
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(iii)     Explain why the primers used in the PCR will bind to panda DNA, but not to DNA from bacteria or bamboo. (line 12)
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(d)     DNA from wild pandas could also be obtained from blood samples. Suggest two advantages of using faeces, rather than blood samples, to obtain DNA from pandas.
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