19. Genetic technology
A section of Biology, 9700
Listing 10 of 107 questions
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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Vitamin A deficiency is a widespread public health problem. One source of vitamin A is carotene in the diet. Carotene can be converted to vitamin A in the body. White rice grains are not a dietary source of vitamin A because they do not contain carotene. Scientists have genetically modified a variety of rice to improve the diet of people who are vitamin A deficient. The grains of this genetically modified rice contain carotene. Describe how genetic engineering could be used to modify a variety of rice so that the grains contain carotene. In a 2018 report, the United Nations Children’s Fund (UNICEF) estimated that: • more than 140 million children are at high risk of vitamin A deficiency • 1.15 million child deaths are caused by vitamin A deficiency each year. Vitamin A deficiency is also a leading cause of childhood blindness. The recommended dietary allowance (RDA) of vitamin A for a 5-year-old child is 400 μg per day. Genetically modified (GM) rice contains 12 μg of carotene per gram of rice. In 2018, four countries approved GM rice as safe to eat. The development of GM rice has been partly paid for by governments. It has been agreed that seeds of GM rice will be made available to farmers in countries with high levels of poverty at the same cost as seeds of normal rice. Some international organisations, such as Greenpeace, campaign against all GM crops. More than 100 respected scientists have asked Greenpeace to stop campaigning against GM rice. Discuss social and ethical arguments that support the position of the scientists.
9700_m21_qp_42
THEORY
2021
Paper 4, Variant 2
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In the USA, about 35% of all maize that is grown has been genetically modified to produce a toxin, called Bt toxin, derived from the bacterium Bacillus thuringiensis. The genetically modified plants are known as Bt maize. Explain the advantages of growing Bt maize. An investigation was carried out into the potential effects of dead leaves from Bt maize on organisms living in streams that flow through areas where the maize is grown. The researchers conducted a laboratory-based experiment in which larvae of one species of aquatic caddis fly, Lepidostoma liba, were fed on non-Bt maize leaves, or on leaves from Bt maize. The growth rates of the larvae were measured. The results are summarised in . 0.0 0.5 1.0 non-Bt maize Bt maize mean growth rate / arbitrary units Describe the effect of eating leaves from Bt maize on the growth rate of L. liba larvae. In a second laboratory-based experiment, three groups of larvae of a different species of caddis fly, Helicopsyche borealis, were fed on pollen containing: A no Bt toxin B Bt toxin at concentrations found in streams in maize-growing areas C Bt toxin at concentrations twice as high as found in those streams. The researchers measured the mortality rates of the caddis fly larvae. Their results are summarised in Table 5.1. Table 5.1 groups compared difference in mortality rate groups A and B no significant difference groups A and C significantly greater mortality in C than in A The researchers were careful to state that their results showed the ‘potential ecological effects’ on the caddis fly larvae of growing Bt maize. Suggest two reasons why ‘potential ecological effects’ is a suitable description of any conclusions that could be drawn from the results of this experiment. When the results of the experiments described in and were published, many other scientists criticised the research very strongly. Suggest why some scientists might wish to suppress results such as these, even if there is no fault with the investigation itself.
9700_s11_qp_42
THEORY
2011
Paper 4, Variant 2
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In the USA, about 35% of all maize that is grown has been genetically modified to produce a toxin, called Bt toxin, derived from the bacterium Bacillus thuringiensis. The genetically modified plants are known as Bt maize. Explain the advantages of growing Bt maize. An investigation was carried out into the potential effects of dead leaves from Bt maize on organisms living in streams that flow through areas where the maize is grown. The researchers conducted a laboratory-based experiment in which larvae of one species of aquatic caddis fly, Lepidostoma liba, were fed on non-Bt maize leaves, or on leaves from Bt maize. The growth rates of the larvae were measured. The results are summarised in . 0.0 0.5 1.0 non-Bt maize Bt maize mean growth rate / arbitrary units Describe the effect of eating leaves from Bt maize on the growth rate of L. liba larvae. In a second laboratory-based experiment, three groups of larvae of a different species of caddis fly, Helicopsyche borealis, were fed on pollen containing: A no Bt toxin B Bt toxin at concentrations found in streams in maize-growing areas C Bt toxin at concentrations twice as high as found in those streams. The researchers measured the mortality rates of the caddis fly larvae. Their results are summarised in Table 5.1. Table 5.1 groups compared difference in mortality rate groups A and B no significant difference groups A and C significantly greater mortality in C than in A The researchers were careful to state that their results showed the ‘potential ecological effects’ on the caddis fly larvae of growing Bt maize. Suggest two reasons why ‘potential ecological effects’ is a suitable description of any conclusions that could be drawn from the results of this experiment. When the results of the experiments described in and were published, many other scientists criticised the research very strongly. Suggest why some scientists might wish to suppress results such as these, even if there is no fault with the investigation itself.
9700_s11_qp_43
THEORY
2011
Paper 4, Variant 3
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Questions Discovered
107