thebiotutor.com 5C Genetic Modification Time: 34 minutes Total marks available: 34 Total marks achieved:
Q1. The picture shows a sheep that has been genetically modified to contain a human gene for making a human protein in its milk. The protein in its milk is a blood clotting substance called factor IX. (a) The process of genetic modification used to produce this sheep involves the use of two types of enzyme. One enzyme cuts DNA and the other enzyme joins DNA. The process also used a vector. (i) Name the enzyme that cuts DNA. (ii) Name the enzyme that joins DNA. (iii) Name a vector. (1) (1) (1) (b) This sheep is transgenic. What is meant by the term transgenic? (c) The transgenic sheep can be reproduced by cloning. (1)
Suggest the advantages of reproducing the transgenic sheep by cloning. (3) (d) (i) Name the small structures in normal plasma that are involved in blood clotting. (1) (ii) Explain why is it important to have blood that clots. (2) (Total for question = 10 marks)
Q2. (a) Describe the stages that are used to genetically modify a bacterium that is able to manufacture human growth hormone. (b) BST is a hormone that increases milk yield in cows. (i) Explain what is meant by the term hormone. (ii) In some countries BST from genetically modified bacteria has been injected into cows to improve milk production. In other countries selective breeding has been used to improve milk production. Describe how selective breeding could be used to increase milk production. (5) (2) (3) (Total for question = 10 marks)
Q3. Describe the stages by which a bacterium can be genetically modified to produce large amounts of a named human protein. (5) (Total for question = 5 marks)
Q4. (a) Describe how micropropagation (tissue culture) can be used to produce large quantities of identical plants. (b) Explain what is meant by the term genetic modification (GM) and suggest why a farmer might want to grow a GM crop. (6) (3) (Total for question = 9 marks) Q1. This question examined knowledge and understanding of genetic modification and cloning. Many candidates were able to recall the names of the enzymes involved in parts (a) (i) and (ii), though the examiners noted that the spelling of restriction and ligase was often incorrect. Candidates were still credited but are encouraged to try to spell biological terms correctly. Less than half the candidates were able to recall the name of a vector in part (iii) as a plasmid or a virus. Those who wrote 'bacteria' alone were given no credit. In part (b), the examiners only gave credit for answers that showed that the gene being transferred came from a different species, not animal or organism. Part (c) posed problems for many candidates. Many failed to produce answers that discussed the transgenic sheep in the question. Listing the sequence of events involved in cloning failed to gain credit as
did general responses discussing the benefits of transgenic techniques or cloning. The examiners rewarded candidates who understood that the advantages of reproducing the transgenic sheep by cloning are that there would be lots of genetically identical sheep producing lots of the factor IX and that there would be no need to repeat the GM procedure. In part (d), most appreciated the role of platelets in blood clotting and that loss of blood is prevented, as is entry of pathogens. Q2. In part (a) students did less well with a few seeming to have no idea about genetic modification. The better responses included extraction of the gene, that codes for growth hormone, from human DNA using a restriction enzyme. Using the same restriction enzyme to cut a bacterial plasmid and using ligase to insert the human gene into the plasmid to make a vector contain recombinant DNA. In part (b)(i) students had to explain what is meant by a hormone. The majority of students earned some credit. The best responses clearly stated that a hormone is released by endocrine glands into the blood stream carried to target cells upon which it has an effect. In part (ii) students had to describe how selective breeding could be used to increase milk production. About half of the answers scored full marks. Some responses had cows mating with other cows, some referred to cloning and some had cows marrying! The best responses described selecting cows with high milk yield and mating these with bulls from mothers who had high milk yield. This process could then be repeated with their offspring for many generations. Q3. There were many outstanding answers to this question, often showing impressive use of correct terminology. There were, however, some who failed to score much credit by simply giving vague references to DNA cutting or irrelevant discussions about fermenters. Sadly, very few actually named a human protein in their answer. Those who did often chose insulin. Q4. There were many excellent answers to part (a) by students who knew all the salient facts about tissue culture, notably the use of explants to culture on nutrient agar under sterile conditions, combined with the further use of plant growth regulators and the provision of sensible abiotic factors. Weaker candidates merely repeated the stem of the question and gained little credit with the rest of their answer. Most often they would confuse tissue culture with some other biological process, often selective breeding. Part (b) was more accessible with most appreciating that the process of genetic modification involved the transfer of genes using enzymes and vectors to produce plants with desirable qualities, most often named as high yielding or pest resistant. Again, weaker candidates wrote about selective breeding and lost credit as a result. They also rephrased the stem of the question and stated that the term genetic modification means that genes are modified. Candidates need to be more aware that rephrasing the stem of a question will not gain credit.
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