A-LevelBiologyGenetic technology9700/42 · Oct/Nov 2022 · Q413 Marks

Haemophilia is a blood clotting disorder in humans caused by a mutant allele on the X chromosome. Table 4.1 compares two forms of haemophilia: haemophilia A and haemophilia B. [Table 4.1]

(a)Genetic engineering is used to make recombinant human proteins to treat people with haemophilia A and haemophilia B. Outline the principles of genetic engineering.[4]
(b)(i)Scientists are working towards a goal of treating haemophilia by gene therapy. They plan to use a common, harmless virus to introduce the functional gene. The virus has a genome that is 4.7 kilobase pairs long. With reference to Table 4.1 and the introduction to (a), assess: • which form of haemophilia, A or B, scientists should try to treat first • whether they should attempt to treat haemophilia with gene therapy at all. Explain your reasoning.[3]
(b)(ii)In gene therapy trials to treat haemophilia, the gene coding for the clotting factor needs to be introduced together with a promoter. Explain why a promoter has to be introduced as well as the desired gene.[2]
(b)(iii)Some individuals taking part in gene therapy trials have been naturally exposed to the virus carrying the functional gene, so that their blood already contains antibodies to the virus. Predict how this will affect the success of the gene therapy treatment.[2]
(c)Gene editing is a newer technique for modifying DNA. Some scientists are researching the use of gene editing, instead of introducing a functional gene, to treat haemophilia. State two possible advantages of using gene editing as a method of treating haemophilia.[2]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2022). The mark or mark type is shown in brackets.

[4] any four from:
1 manipulate DNA to modify organism's characteristics / AW ;
2 gene/ allele / (section of) DNA, obtained using restriction, enzyme / endonuclease ;
3 use of reverse transcriptase to make, gene / allele / (section of) DNA, using mRNA ;
4 gene / allele / (section of) DNA, inserted into, vector / plasmid, using ligase ;
5 add/insert, (recombinant), vector / plasmid, into, (host) cell / bacterium ;
6 clone/multiply, cell / bacteria; A put bacteria in a fermenter
7 gene is expressed and, protein / factor XIII / factor IX, is made ;
8 AVP; e.g. artificial / chemical, synthesis of new gene
[3] any three from:
1 haemophilia B (first) because (F9) gene is small enough to fit into virus / 1.6kbp and 4.7kbp; ora
2 haemophilia A (first) because it is more common ; ora
therapy not attempted
3 (because) disease can be managed by recombinant proteins ;
4 gene therapy (trials) involve, risk of harm / side effects / allergic reactions / immune response ;
therapy attempted
5 provides a cure / AW ;
6 taking clotting factors etc. can involve risk of harm;
[2] any two from:
1 to allow binding of, RNA polymerase / transcription factors ;
2 to switch gene on / so gene is expressed / allow transcription (of gene) ;
3 at right time / all the time / in sufficient quantities ;
4 in correct tissue ;
[2] any two from:
decrease success because:
1 antibodies / immune response, may, destroy / attack / AW, virus / vector ;
2 (so) limiting / stopping, delivery of, gene / allele / DNA, to cells ;
3 destroys GM cells or destroys cells that have successfully taken up the, virus / gene / allele / DNA ;
[2] any two from: list rule
1 (gene editing) is, precise / exact / accurate;
2 patient's own gene can be, edited / corrected or no introduction of, gene / allele;
3 no need to introduce promoter ;
4 less/no, risk of cancer or less/no, immune response ;