Manipulating Genomes (OCR A Level Biology): Exam Questions

Genes isolated from DNA can be used in gene therapy.

Cystic fibrosis (CF) is a disease that could be treated using gene therapy.

Healthy individuals have a gene that codes for a channel protein, called CFTR, found in the plasma membrane of a variety of cells, including those lining the airways of the lungs.

People suffering from CF have two copies of a recessive allele and so their cells do not synthesise the correct channel protein.

The allele that codes for the functioning CFTR protein can be inserted into the DNA of CF sufferers. The cells can then synthesise the correct CFTR protein and function as normal.

(i) The treatment of cystic fibrosis is described as somatic gene therapy. Another type of gene therapy is known as germ-line gene therapy.

Complete the table below to show three differences between somatic gene therapy and germ-line gene therapy.

[3]

(ii) Some attempts at gene therapy have resulted in changes to the functioning of other genes.

Explain how inserting a new gene into a chromosome could affect the functioning of other genes in that chromosome.

[2]

(iii) CF occurs when individuals have two copies of a recessive allele.

Huntington’s disease is a lethal disease caused by a dominant allele that codes for the protein huntingtin.

Suggest why gene therapy is unlikely to work as a treatment for Huntington’s disease.

[1]

Fred Sanger developed an effective DNA sequencing technique in 1977.

Define the term DNA sequencing.

The speed at which DNA can be sequenced has been increasing rapidly since the introduction of DNA sequencing.

The length of DNA that can be sequenced in a given time is measured in base pairs or kilobase pairs.

In 1980, the speed at which DNA could be sequenced by a single machine was approximately 500 base pairs per hour. In 2016 that speed had increased to approximately 50 million kilobase pairs per hour.

Calculate how many times faster the speed of DNA sequencing is in 2016 compared with 1980.

Answer............................... times faster

One technique that has allowed the speed of DNA sequencing to increase has been the development of nanopores.

Fig. 21 shows how nanopores can be used to sequence DNA.

Fig. 21

(i) State one development, other than nanopore technology, that has led to an increase in the speed at which DNA can be sequenced.

[1]

(ii) Part of Fig. 21 is labelled G.

Use the table below to identify two differences between the part labelled G and the structure of a molecule of ATP.

[2]

(iii) Explain how DNA sequencing allows the sequence of amino acids in a polypeptide to be predicted.

[2]

DNA sequencing can be used to determine the genome of an entire organism. The first organism to have its entire genome sequenced was a virus. Ebola is a virus that caused the death of over 11000 people in West Africa between 2014 and 2016. The DNA of ebola virus has a rapid rate of mutation. Since the first outbreak in 2014 scientists have been working to develop an effective vaccination against ebola. Other scientists have developed a portable nanopore sequencing technique that could be used to sequence rapidly the entire ebola genome. Outline how DNA sequencing and bioinformatics could be used to increase the effectiveness of a vaccination programme against ebola.

sequencing ..............................................

bioinformatics ................................................

Fig. 21 shows some of the steps involved in producing a genetically modified bacterium.

Fig. 21

The following passage describes steps A and B. Complete the passage using the most appropriate terms.

A gene is cut from the DNA of the donor organism using a ........................... ........................... .

The .................................. enzyme is used to cut open a small piece of bacterial DNA so that the base sequences at the end of each piece of DNA are .................................. .

Describe the events that are taking place at the step labelled C.

Step D results in a transformed bacterium.

Many individual bacteria are not transformed successfully during this procedure.

Explain how scientists can determine the success of step D in this procedure.

Bacteria can be genetically modified to produce human insulin.

The process is similar to that shown in Fig. 21 with some differences.

First, instead of isolating DNA that contains the insulin gene, mRNA that codes for insulin is extracted from human pancreas cells.

What needs to be done with the mRNA in order for the rest of the genetic modification to be completed?

Some people are concerned about genetic modification.

State one valid concern that people have about the genetic modification of bacteria.

The European corn borer moth, Ostrinia nubilalis, is a pest of agriculture. Its larvae develop inside maize stems and eat the contents, weakening the stems so that the plants collapse.

The bacterium Bacillus thuringiensis (‘Bt’) produces a protein that poisons the larvae of moths and butterflies. This protein can be isolated from cultures of Bt and packaged in fluids to be sprayed on the surface of plants.

The gene coding for the toxic protein has also been isolated. It has been incorporated into a genetically modified strain of maize called Bt corn. This makes the plant tissues poisonous to the corn borer moth.

Consider the statement:

Outline one experiment or investigation that would provide evidence to support or contradict the statement.

A farmer wants to increase the yield of maize.

A friend recommends planting genetically-modified Bt corn as it would be more effective against European corn borer larvae rather than spraying unmodified corn with Bt toxin.

Which method would you recommend to the farmer? Justify your answer.

Some students investigated the different ways of protecting maize plants against the corn borer moth.

In each of three separate but close-together square plots, in the same field, they planted several hundred maize seedlings.

Plot A: untreated (control).
Plot B: sprayed daily with Bt toxin.
Plot C: the seedlings planted were genetically modified Bt corn.

On the first day of each week, one student would walk around the edge of a plot and count the number of maize plants that had collapsed in that plot. Each plot had a student responsible for counting. The results are shown in Table 20.1.

Table 20.1

The students’ tutor raised a number of concerns about the investigation. In summary:

• The methods were not a valid test of what was being investigated.

• The results may not be accurate.

• Some variables were not controlled.

Explain why these concerns are justified and suggest improvements to the investigation.

Many plants can produce natural clones of themselves. Gardeners and farmers take advantage of this natural process by taking cuttings.

When a genetically modified plant is created, it may be cloned into many plantlets in the process called micropropagation.

Compare the equipment and techniques of taking cuttings with those used for micropropagation.