19.2. Genetic technology applied to medicine
A subsection of Biology, 9700, through 19. Genetic technology
Listing 10 of 37 questions
shows the CFTR (cystic fibrosis transmembrane conductance regulator) protein in a plasma (cell surface) membrane. Describe the normal function of the CFTR protein. On , use the letter E to indicate the external face of the membrane. State how you identified this face. Cystic fibrosis is caused by a recessive allele of the CFTR gene. Explain the meaning of the term recessive allele. Explain how cystic fibrosis affects the function of the lungs. As cystic fibrosis is caused by a recessive allele of a single gene, it is a good candidate for gene therapy. Trials were undertaken in the 1990s, attempting to deliver the normal allele of the CFTR gene into cells of the respiratory tract, using viruses or liposomes as vectors. Explain how viruses deliver the allele into cells. In some people with cystic fibrosis, the allele has a single-base mutation which produces a ‘nonsense’ codon within the gene. Explain how this mutation would prevent normal CFTR protein being produced. A new type of drug, PTC124, enables translation to continue through the nonsense codon. Trials in mice homozygous for a CFTR allele containing the nonsense codon have found that animals treated with PTC124 produce normal CFTR protein in their cells. The drug is taken orally, and is readily taken up into cells all over the body. Using your knowledge of the progress towards successful gene therapy for cystic fibrosis, suggest why PTC124 could be a simpler and more reliable treatment for this disease.
9700_w08_qp_4
THEORY
2008
Paper 4, Variant 0
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Severe combined immunodeficiency (SCID) is a group of life-threatening diseases. SCID is caused by mutations that prevent the normal function of the immune system. Infants born with SCID are at very high risk of infectious diseases. One feature of SCID is that T-lymphocytes do not develop normally. In the development of normal T-lymphocytes, the production of circular pieces of DNA called T-lymphocyte receptor excision circles (TRECs) is an important event. It is possible to use the polymerase chain reaction (PCR) to detect TRECs in DNA extracted from a sample of blood. The results of this reaction can be used to identify children with SCID. Describe the role of the primers in the PCR used for the detection of TRECs. Suggest and explain how the results of PCR for the detection of TRECs can be used to identify children with SCID. Before 2010, children in the United States of America (USA) were tested for SCID either: • if someone in their family history had SCID, or • if they developed several infections in a short space of time. From 2010, the USA started to introduce a screening programme for SCID, in which children were tested soon after birth. By 2016, the screening programme was used for nearly all children in the USA. shows the percentage contribution of each of these three approaches to the identification of children with SCID from 2010 to 2016 in the USA. percentage contribution to the identification of children with SCID 2010 2011 2012 2013 year 2014 2015 2016 key family history infections screening programme With reference to , describe how the contribution of the three approaches to the identification of children with SCID changed from 2010 to 2016. Suggest the advantages of screening all children for SCID soon after birth. One form of SCID is caused by a mutation that results in a deficiency of the enzyme adenosine deaminase (ADA). Children with ADA-deficient SCID can be treated with gene therapy using a virus. After successful gene therapy, the children are able to produce ADA for themselves. Suggest how children with ADA-deficient SCID can be treated with gene therapy using a virus. Outline the challenges of using a virus for gene therapy.
9700_m20_qp_42
THEORY
2020
Paper 4, Variant 2
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Neurofibromatosis (NF) is a genetically inherited condition in humans where tumours grow in the nervous tissue. One symptom, which can develop around the age of 20 years, is loss of sight due to tumours on the optic nerve. If one parent has NF, there is at least a 50% chance that his or her children will develop the condition, even if the other parent is unaffected. Complete the genetic diagram below to show how NF may be transmitted from parent to child. key to symbols parental phenotypes parent with NF unaffected parent parental genotypes gametes offspring genotypes offspring phenotypes Suggest how a person may develop NF when there is no family history of the condition. Suggest how a tumour on the optic nerve could prevent the transmission of nerve impulses to the brain.
9700_s14_qp_42
THEORY
2014
Paper 4, Variant 2
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Questions Discovered
37