Gene Technologies (A Level only) (AQA A Level Biology)

Seven skeletons were discovered in a house in Pompeii, three of which were children. It is believed they were inhabitants and workers within the house when Mount Vesuvius erupted on 24 October 79 AD. Researchers were able to isolate very small amounts of  DNA from these skeletons. The DNA obtained was used in the polymerase chain reaction (PCR). Genetic fingerprinting was then carried out on this DNA to identify the skeletons.

Figure 1 shows some of the results of the genetic fingerprinting of the three children and four adults.

Figure 1

Explain why the researchers used polymerase chain reaction in their investigation.

During the polymerase chain reaction method, DNA is heated to 94 °C and DNA primers, nucleotides and enzymes are added to the mixture.

(i) Explain why the DNA is heated to 94 °C.

(ii) Describe what is meant by DNA primers and explain why these are added during the polymerase chain reaction.

(iii) State why the enzymes used in the polymerase chain reaction must be thermostable.

It was determined that the three children were siblings and shared the same biological parents. Their mother is Adult B.

Suggest which of the other adults is the children’s father and give the reason for your answer.

Describe the method by which genetic fingerprinting is undertaken.

Spinocerebellar Ataxia is a genetic condition that leads to a loss in the brain’s ability to coordinate the movement of hands, eye and in speech. The gene involved contains a section of DNA with many repeats of the base sequence CAG. The number of these repeats determines whether or not an allele of this gene will cause Spinocerebellar Ataxia.

Figure 1 shows the age at which a sample of patients with Spinocerebellar Ataxia first developed symptoms and the number of CAG repeats in the allele causing Spinocerebellar Ataxia in each patient.

Figure 1

People can be tested to determine the number of CAG repeats on this allele. Some scientists suggest that the results in Figure 1 can be used to predict whether an individual will develop Spinocerebellar Ataxia and at what age.

Use the information in Figure 1 to evaluate this suggestion.

Using the information in Figure 1, suggest why the allele that causes Spinocerebellar Ataxia is passed on in human populations despite the condition being fatal.

DNA samples were taken from four people, W, X, Y and Z. Polymerase chain reaction (PCR) was used to produce many copies of the section of DNA containing CAG repeats obtained from each person. The DNA fragments were then separated by gel electrophoresis and detected by a radioactively labelled probe. Figure 2 shows the appearance of part of the gel after an X-ray was taken. The bands show the DNA fragments that contain the CAG repeats.

Figure 2

Each individual usually has two bands. Suggest why only one band was seen for Person X.

Only one of the four people (W, X, Y and Z) tested positive for Spinocerebellar Ataxia.

Suggest which person this was and explain your answer.

A scientist used a restriction enzyme to cut a section of mouse DNA into multiple pieces.The enzyme produced a staggered cut. A scientist wanted to insert these pieces of DNA into plasmids and used the same restriction enzyme to cut the plasmids. Explain why the pieces of mouse DNA would be able to join to the cut DNA of the plasmids.

Name the other enzyme the scientist added to the mixture to form recombinant plasmids and describe its function.

The plasmid formed from this experiment is used as a vector. Define the term vector when used in this context.

Before choosing a plasmid to use, the scientists ensured it contained antibiotic resistance genes.

Explain the reason for this.

Farmers use genetic engineering to quickly introduce genes that benefit the health and value of their livestock. Protein Q is a protein that gives pigs resistance to a disease that is killing livestock. Goats can be genetically engineered to produce Protein Q in their milk.

Figure 1 shows the stages involved in this process.

Figure 1

The zebrafish gene attached to the pig Protein Q gene codes for a protein that glows blue under fluorescent light. Explain why this gene has been attached.

State the role of a promoter and suggest why a goat promoter specific to the milk gland was used instead of a pig promoter.

There are very few live births that result from the multiple embryos that are implanted.The likelihood of producing offspring from genetically modified eggs is low. Suggest one reason why few live births result from the many embryos that are implanted.

When pigs are bred in farms, it is important to ensure only unrelated pigs breed. Suggest how genetic fingerprints might be used to do this.

A researcher wants to detect and measure accurately the amount of RNA present in a liver tissue sample in order to determine the types of proteins being expressed. They do this by RT-PCR (reverse transcriptase-polymerase chain reaction).

RT-PCR uses a reaction mixture containing:

•       the sample for testing

•       DNA polymerase

•       primers

•       reverse transcriptase

•       DNA nucleotides

•       fluorescent dye

Explain the roles of DNA polymerase and reverse transcriptase in RT-PCR.

Before commencing the experiment, the researcher adds hydrolytic enzymes to the sample to ensure all DNA is hydrolysed. Explain why the researcher carries out this step.

DNA replication eventually stops in the polymerase chain reaction.

Suggest one reason why this is.

Researchers have used the RT-PCR method to detect the presence of different hepatitis viruses, which are a family of RNA viruses that affect the liver.

Explain why the researchers produced a variety of primers for this procedure.

Salty soils can inhibit the growth of crop plants, such as tomatoes, particularly in coastal areas. Scientists have genetically modified some species of tomato to increase their salt tolerance. Figure 1 shows the process used to introduce a gene for a sodium-pump protein, into the genome of tomato plants. The gene resulted in increased tolerance of the tomato plants to high salt soil, without affecting the taste or salt content of the fruit produced.

Figure 1

Describe three methods that could be used to obtain the DNA fragment which contains the gene for the sodium pump protein.

In the process shown in Figure 1, the required gene sequence is extracted from Arabidopsis and is inserted into the tomato plant.

Explain why the transgenic tomato plant is able to produce the sodium pump protein despite being a different species to the donor plant.

Suggest two possible ways that cells with the sodium pump gene might be selected in stage 4 of Figure 1.

Explain the evidence from Figure 1 that the genetically modified tomato plant cells are totipotent.

Use the information provided above along with your own knowledge to answer the Following.

Suggest and explain how a mutation, such as the Philadelphia mutation, could be acquired later on in life (lines 5-6).

The BCR-ABL test is available only to patients who have been diagnosed with leukemia (lines 10-11). Suggest how genetic screening may be valuable in the treatment of patients with the philadelphia mutation.

Outline how scientists could use polymerase chain reaction (PCR) in combination with a labelled gene probe to detect the presence and quantity of the philadelphia fusion gene (lines 14-15).

Outline the role of a genetic counsellor (line 19-20).

Wild boars are found across many European countries. Scientists studied the genetic diversity of these boar by comparing the variable number tandem repeats (VNTRs) of the mitochondrial DNA. Mutations can cause variation in the mitochondrial VNTRs. Table 1 shows the results of their study.

Table 1

 Suggest why differences in VNTR on mitochondrial DNA can be used to establish diversity.

Explain how genetic fingerprinting could be used to make comparisons between the VNTR sequences in the different boar populations.

Organisms can protect their own cellular DNA from the action of restriction endonucleases by methylation of the adenine and cytosine.

Use your knowledge of enzyme action to explain this observation

One restriction enzyme is used to cut a sample of the DNA from the mitochondrial DNA of a wild boar. The resulting genetic fingerprint can be seen in Figure 1.

Figure 1

State how many times that enzyme made a cut in the DNA and justify your answer.

Genetic engineering can be used to create insulin for patients suffering from type 1 diabetes. The process involves the use of bacterial vectors in the process shown in Figure 1.

Figure 1

Suggest why bacterial cells are used in the production of human insulin for diabetic patients.

Explain how antibiotic resistance genes can be used to make sure that the only bacteria which are replicated are those which have taken up the modified plasmids containing the insulin gene.

Compare the use of in vivo gene cloning compared to in vitro gene cloning for the production of gene fragments.

Historically, insulin extracted from pigs was used to treat diabetics.

Suggest why it may be more desirable to use modern gene technology methods to produce insulin for diabetic patients rather than using animal insulin.

A plantibody is an antibody which is produced by a plant which has been genetically engineered using an animal gene for a desired antibody.

Suggest how plantibodies could be used to combat disease in humans.

With reference to the enzymes involved, describe how the antibody gene discussed in part (a) could be isolated from an animal cell and introduced into a crop plant such as maize.

An alternative way to isolate the required antibody gene sequence is using a gene Machine. When using a gene machine, scientists must consider the biosafety and biosecurity of the sequence being created.

Suggest what is meant by this.

Evaluate the use of recombinant DNA technology to treat disease.