Genetic engineering

The use of genetically modified (GM) crops in agriculture raises certain concerns.

What is not a valid concern about the use of GM crops in agriculture?

A Eating modified genes is harmful to consumers.

B Modified genes might spread to wild populations.

C Patenting of GM crops by large companies might disadvantage independent producers in developing countries.

D Pests might evolve resistance to pesticides contained in GM crops.

RNA and DNA are polynucleotides.

Two types of RNA are messenger RNA and transfer RNA.

The table shows some properties of these two types of RNA.

Place ticks (✓) in the correct boxes to indicate which properties are true for each type of RNA.

Outline how gene expression is regulated within cells at the post‑transcriptional level.

A student writes this method for extracting DNA from animal cells:

1. Grind the sample of cells using a mortar and pestle.

2. Mix the sample with detergent.

3. Add ethanol to precipitate the DNA from the solution.

4. Spool the DNA onto a glass rod.

Another student suggests that step 1, grinding the sample of cells, is unnecessary.

Explain why step 1 is unnecessary.

State one other step that the student should include in the method and explain why this step is necessary.

Electrophoresis is used to separate fragments of DNA so that the separated DNA fragments can be compared and analysed.

The diagram shows an electrophoresis box. Solutions of DNA samples have been added to three of the wells in the box.

Solutions containing

State two other solutions that should be added to the box before performing electrophoresis and explain the purpose of each solution.

Electrophoresis can be used to detect disease‑causing alleles, such as the mutant HBB allele that causes sickle cell disease.

Restriction enzymes are used to produce fragments of HBB alleles for analysis by electrophoresis.

These restriction enzymes:

• produce one fragment when the sickle cell HBB allele is present

• produce two smaller fragments when the normal HBB allele is present.

The diagram shows the results of electrophoresis of DNA samples from five people. It only shows DNA fragments from the HBB gene.

State the lane numbers that indicate:

• a genotype that is homozygous for the sickle cell HBB allele

• a genotype that is homozygous for the normal HBB allele

• a heterozygous genotype for the HBB gene.

Homozygous sickle cell........

Homozygous normal........

Bacterial cells can be used for genetic engineering.

A donor gene is placed into a plasmid, which is taken up by a bacterial cell.

This process is inefficient. Not all plasmids form recombinant DNA with the donor gene, and only a small percentage of bacterial cells take up plasmids.

A scientist estimates that 40% of their plasmids join to the donor gene to form recombinant DNA.

One in 2500 bacterial cells takes up a plasmid to form a transformed bacterial cell.

The scientist uses 1 × 10⁹ bacterial cells.

Calculate the number of cells that take up a plasmid containing the donor gene.

The percentage of plasmids that are taken up by bacterial cells is known as the transformation efficiency.

Suggest one factor that scientists could change to improve transformation efficiency.

6 ‑thalassemia is an inherited blood disorder in which the ‑globin chain of haemoglobin is changed or absent in a person’s red blood cells.

Many different DNA mutations in the ‑globin gene can cause ‑thalassemia, including these two mutations:

Each mutation occurs in a triplet in the template strand of DNA.

The transcribed mRNA is complementary to the template strand.

The diagram on the opposite page is a representation of the genetic code. It shows the amino acid encoded by each mRNA codon.

The letters in the centre of the diagram represent the first base in each codon.

State the amino acids that are encoded by the original triplet and the mutated triplet in mutation 1.

Original amino acid........

State and explain the effect of mutation 2 on the structure of the ‑chain of haemoglobin.

* In 2023, a gene editing treatment for ‑thalassemia was approved for use in the UK.

Gene editing is a form of gene therapy.

Standard gene therapy:

• uses a vector to deliver a functional, normal allele to cells in a person’s body

• does not remove the faulty, disease‑causing allele from the person’s cells.

Gene editing:

• can correct the faulty, disease‑causing allele so that only the functional, normal allele is present at that locus

• can be performed on stem cells that have been removed from a person’s body; the stem cells are then transferred back into that person.

Discuss the advantages of gene editing compared to standard gene therapy and discuss the ethical issues shared by both forms of gene therapy.

Extra answer space if required.

Bioinformatics, computational biology and synthetic biology are relatively new techniques in biology that have a variety of uses.

This is a preserved thylacine, Thylacinus cynocephalus, a large Australian carnivore that became extinct in 1936.

Many preserved thylacine specimens in museums contain DNA. Scientists have used DNA sequencing, bioinformatics and computational biology to reconstruct the genome of the thylacine. Some scientists hope to be able to use bioinformatics and synthetic biology to produce a living thylacine in the future.

Much of the thylacine DNA present in the museum specimens has broken down. In order to assemble an entire thylacine genome, it is necessary to supplement the thylacine DNA with DNA from a living close relative of the thylacine.

The thylacine belonged to the order Dasyuromorphia. The table shows the classification of the thylacine and some living species of the order Dasyuromorphia.

Name the classification taxon represented by the column headed A.

Using the information in the table, describe the evolutionary and genetic relationships between the species that are listed.

Explain why it is difficult to decide which of the other species would be the most appropriate to use as a source of DNA for constructing a thylacine genome.

All the species in the table belong to the animal kingdom.

Other than the presence or absence of vacuoles, state two features of the cells of these multicellular organisms that would mean they could be classified only in the animal kingdom.

Synthetic biology involves re-designing organisms for useful purposes. One such purpose could be the production of useful proteins.

Proteins can be produced by traditional genetic engineering but the range of proteins available is limited to those that are already produced by a living organism.

Bioinformatics and computational biology can be used in the production of new proteins that are not found anywhere in nature.

* Explain how gene sequencing, bioinformatics and computational biology are used in the production of useful proteins in synthetic biology.

Extra answer space if required.

Suggest why some people might be concerned about the increase of synthetic biology.

The thylacine finally became extinct in 1936 as a result of hunting by humans. However, its population had been in decline for many years before.

Some scientists have concluded that the thylacine was particularly vulnerable to extinction because of low genetic diversity within the species.

The table shows the proportion of heterozygous loci in a range of Australian mammal species together with information about how endangered they are.

Describe the evidence in the table that supports the conclusion that low genetic diversity contributed to the extinction of the thylacine.

Identify one piece of evidence that does not support the conclusion that low genetic diversity contributed to the extinction of the thylacine.

Type 1 diabetes mellitus is characterised by a lack of insulin production. Type 2 diabetes mellitus can involve reduced production of insulin and a decreased response to insulin.

* Scientists analysed the occurrence of diabetes in identical and non-identical twins.

Identical twins have the same DNA. Non-identical twins share approximately 50% of each other’s DNA.

The scientists selected 614 pairs of twins in which at least one of the individuals had diabetes: 109 pairs had type 1 diabetes; 505 pairs had type 2 diabetes.

The scientists calculated the percentage probability of an individual having diabetes when their twin has the disease.

The table shows the percentage probability of both individuals in a pair of twins developing either type 1 or type 2 diabetes.

Explain what conclusions can be drawn from the data in the table about the influence of the environment and genetics on the probability of developing diabetes.

Extra answer space if required.

Insulin is secreted from cells in the pancreas.

This is a photomicrograph of pancreatic tissue.

Identify the structures labelled A, B and C.

The graph shows the changes in the rate of insulin secretion in a person with type 2 diabetes after consuming glucose.

The table shows the changes in the rate of insulin secretion in a person with normal glucose tolerance after consuming glucose.

Plot the data from the table on the graph and draw a line of best fit.

The table lists statements about a molecule of insulin.

Complete the table by stating the level of protein structure (primary, secondary, tertiary or quaternary) to which the statement relates.

Bacteria can be genetically modified to produce insulin.

State how a plasmid containing the gene coding for insulin can be transferred into a bacterial cell.

Suggest how bacterial cells can be screened to check if they have taken up a recombinant plasmid.

In the future, type 1 diabetes could be treated by giving patients new pancreatic -cells that have been produced in a laboratory from stem cells.

State a feature of stem cells that allows them to be used to produce pancreatic -cells.

Future treatments for type 1 diabetes may be able to use stem cells from a patient’s body to produce new -cells.

Explain why patients receiving these new -cells would still need to be given immunosuppressant drugs.

Genetic modification and selective breeding can be used to improve the characteristics of crop plants, such as maize.

In high light intensity, photosystem II absorbs excess light energy.

A process called nonphotochemical quenching (NPQ) converts the excess light to heat energy.

NPQ can continue when light intensity is no longer in excess. This makes photosynthesis inefficient.

Scientists genetically modified (GM) crop plants to limit NPQ.

The scientists exposed unmodified plants and GM plants to a period of high light intensity followed by lower light intensity. The scientists then compared the rate of NPQ and the rate of carbon dioxide (CO₂) fixation in unmodified plants and GM plants.

Some of the results are shown in the table.

State one dependent variable in this investigation.

Explain the effect of genetic modification on the rate of CO₂ fixation after 150 seconds of low light intensity.

Often a single company holds the patent for a GM crop plant.

Suggest a potential ethical issue that may exist if one company holds the patent for a GM crop plant.

Humans have been selectively breeding maize as a crop plant for thousands of years, which has resulted in many different varieties of maize.

Different varieties of maize have different genomes.

Describe how bioinformatics and computational biology can be used to compare the genomes of different varieties of maize.

Two characteristics that farmers have selectively bred in maize are colour and kernel (fruit) shape.

Colour is determined by a gene with two alleles:

• Allele A is dominant and results in a purple colour.

• Allele a is recessive and results in a yellow colour.

Kernel shape is determined by a gene with two alleles:

• Allele B is dominant and results in a smooth shape.

• Allele b is recessive and results in a wrinkled shape.

The two genes are found on different chromosomes.

Two maize plants are crossed.

• One parent plant is purple and smooth and heterozygous for both genes.

• One parent plant is yellow and smooth and heterozygous for gene B/b.

Complete the answer lines below to show this genetic cross.

Parental genotypes:........ ........

Expected offspring phenotypes:........

Expected phenotypic ratio:........

The heart can be affected by a variety of disorders, some of which involve the immune system.

Fig. 1.1 shows the roles of three different types of antibody, labelled R, S and T.

R S

Harmful molecules released by pathogens Fig. 1.1

State the names of the three different types of antibody shown in Fig. 1.1.

A condition called rheumatic heart disease can occur when a person’s antibodies attack antigens on their own heart cells.

State the name of the type of disease represented by rheumatic heart disease.

Fig. 1.2 shows two electrocardiogram (ECG) traces:

• an ECG of normal heart activity

• an ECG of a person with a type of heart disease

Fig. 1.2

Describe how the ECG trace of the heart with heart disease is different from the ECG trace of a normal heart.

Gene therapy is a possible future treatment for heart disease.

The AC6 gene codes for one form of the enzyme adenylyl cyclase.

Clinical trials have tested the effect of increasing levels of the AC6 gene in heart cells.

Suggest how using gene therapy to increase levels of the AC6 gene in heart cells may improve heart function.

State one method for inserting the AC6 gene into the heart cells during gene therapy.

The results from gene therapy trials are published in peer-reviewed journals.

State why the results from gene therapy trials are published in journals.

Haemoglobin is an important protein in many animals, including humans.

Sickle cell disease (SCD) is a disease caused by the production of abnormal haemoglobin.

A treatment for SCD is based on a technique called CRISPR gene editing and allows SCD patients to begin production of fetal haemoglobin.

The treatment has the following steps:

• Bone marrow stem cells are removed from the patient with SCD.

• An enzyme called Cas9 is added to the stem cells.

• Cas9 deletes bases from the BCL11A gene.

• The BCL11A gene usually switches off the fetal haemoglobin gene in adults.

• The gene-edited stem cells are placed back in the patient.

• The patient can now produce fetal haemoglobin.

This CRISPR gene editing method is different from traditional genetic engineering, which uses restriction enzymes and plasmids.

Describe the similarities and other differences between CRISPR gene editing and traditional genetic engineering methods.

Haemoglobin plays a crucial role in transporting oxygen in animals. Several ions also have roles in oxygen transport.

Three ions are listed in the table below.

Place ticks (✓) in the correct boxes to indicate which properties and features are true for each ion.

Prokaryotic cells have cytoskeletons. The molecules in prokaryotic cytoskeletons are different from the molecules in eukaryotic cytoskeletons.

Table 4.1 lists three molecules present in a prokaryotic cytoskeleton.

Suggest the function of Protein A.

Suggest the function of Protein C.

An antibiotic called A22 binds irreversibly to Protein B. Despite its antibiotic properties, A22 is not used in humans.

Suggest why scientists have advised that A22 should not be used in humans.

Vancomycin is an antibiotic that has been used to treat bacterial infections for many decades. Several strains of bacteria have evolved resistance to vancomycin.

Oritavancin is an antibiotic with a similar structure to vancomycin.

Table 4.2 shows data obtained from treatments with the two antibiotics.

Use the data in Table 4.2 to evaluate the advantages and disadvantages of using oritavancin rather than vancomycin as an antibiotic.

Complete the diagram above by writing the missing words or phrases in the boxes labelled X, Y and Z.

........ Answer on the diagram........

Suggest why the scientists used a plasmid that contained an antibiotic resistance gene.

The scientists observed the following:

• 1 in 400 bacteria took up the plasmid

• 1 in 1000 of the plasmids taken up by bacteria contained the ‑galactosidase gene.

Calculate the percentage of bacteria that contained the ‑galactosidase gene.

A technique called quantitative PCR is used to check that the E. coli population is growing on the mice liver tumours rather than on healthy tissue.

Suggest how the scientists could use PCR to compare E. coli growth rates on cancerous liver tissue and healthy tissue.

Some people think that the genetic engineering of certain organisms is unethical.

However, there are very few ethical concerns about the genetic engineering of bacteria such as E. coli.

Suggest why there are very few ethical concerns about the genetic engineering of E. coli

Which of the following is not a valid concern about the use of genetic modification?

A that antibiotic resistance genes could transfer to pathogenic bacteria

B that herbicide resistance genes could be transferred to wild species

C that certain seeds might not be available for use by poor farmers

D that the use of human embryos in stem cell production is unethical

Your answer

DNA can be obtained from a variety of plant and animal cells.

A group of students tried to purify some DNA from leek cells using the following method. They decided that exact volumes were not necessary.

State the purpose of step 1.

Suggest why a protease enzyme added in step 3 is needed to purify DNA.

The students considered using pineapple juice as a source of protease enzyme.

Suggest why this would not be an appropriate source of protease when attempting to produce a pure sample of leek DNA.

State one important step that the students had left out of their method.

Name the process described in step 6.

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.

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.

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.

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.

Which of the following statements about gene therapy is not correct?

A changes resulting from gene therapy cannot be passed on to offspring

B germ-line gene therapy affects the whole organism

C gene therapy is a form of genetic engineering

D somatic cell gene therapy can only affect a limited number of cells

Your answer

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

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.