19. Genetic technology
A section of Biology, 9700
Listing 10 of 107 questions
In 1984, the geneticist Alec Jeffreys invented a DNA testing technique, known as DNA profiling, that produces a DNA banding pattern on a gel. The DNA banding pattern is unique to each individual. DNA profiling can be used in police forensic work to catch criminals. Since 1987, police in many countries have collected and stored DNA from crime scenes to create DNA profiles, which they try to match with the DNA profiles of criminal suspects. DNA at a crime scene may be obtained from hairs and traces of blood, semen and saliva. Explain why PCR may be needed before DNA from a crime scene can be profiled. Explain why electrophoresis produces a DNA banding pattern on a gel. GEDmatch is described as ‘an open data personal genomics website’. It can be used by people who want to upload their DNA data to trace their ancestors and other relatives. In 2018, police in the USA solved a large number of serious crimes. Some of these crimes had been unsolved for over thirty years. The police used GEDmatch to profile DNA taken from crime scenes and to look for matching DNA profiles. In many cases the police found partial matches to the relatives of criminals. This allowed the criminals to be identified and then charged on the basis of a complete DNA profile match. Suggest why the police strategy of comparing crime scene DNA with the GEDmatch database was so successful. Explain why GEDmatch is an example of bioinformatics. The first successful conviction resulting from the use of GEDmatch by the police was widely reported. Some journalists and broadcasters thought that the GEDmatch website should not have been used by the police in this way. In the days following the news, the number of citizens choosing to upload their DNA data to GEDmatch increased from 1500 to 5000 a day. Comment on the social and ethical issues raised by this first successful conviction.
9700_w21_qp_43
THEORY
2021
Paper 4, Variant 3
View
The bacterium Escherichia coli divides once every 50 minutes at 36 °C. E. coli were grown on a medium containing only heavy nitrogen, 15N, until all of the bacterial DNA contained heavy nitrogen. Some of the bacteria were moved from a heavy nitrogen medium and cultured in a medium with only light nitrogen, 14N (0 minutes). These bacteria continued to reproduce and samples were extracted and centrifuged at regular intervals. Hybrid DNA contains both heavy and light nitrogen. The diagram shows the possible positions (upper, middle and lower) of the bands of DNA. The actual positions of bands in the first two samples are shown...
9700_w22_qp_13
MCQ
2022
Paper 1, Variant 3
View
Use A husband and wife who already have a child with cystic fibrosis (CF) elected to have their second child tested for the condition while still a fetus in very early pregnancy. The results of the test, a DNA banding pattern, were discussed with a genetic counsellor. The relevant DNA banding pattern produced by electrophoresis is shown in . father first child fetus mother direction of movement of DNA fragments electrophoresis gel band of DNA With reference to , explain why, the fetus will develop CF, the positions of the bands of DNA of the first child and of the fetus indicate that the mutant allele for CF has a deletion in comparison with the normal allele. Explain briefly the need to discuss the result of the test with a genetic counsellor.
9700_w09_qp_41
THEORY
2009
Paper 4, Variant 1
View
Cancer is a disease in which normal controls over cell division are lost and malignant tumours form. An early diagnosis of many types of cancer can result in successful treatment. The BRCA2 protein is involved in suppressing the development of tumours. The gene that codes for this protein is on chromosome 13. Several different dominant alleles of this gene, BRCA2, code for faulty versions of the protein. The presence of any one of these faulty alleles leads to an increased chance of developing several types of cancer, including breast cancer. Not everyone with one of these alleles develops cancer. This is because environmental factors, including lifestyle, are also involved. is a pedigree (family tree) showing the occurrence of cancers in four generations of a family. The presence of a faulty BRCA2 allele was confirmed in person 15. The other individuals with cancer were not tested for the presence of the allele. Individuals 24–30 are all under twelve years old. female cancer allele present but no cancer no information male cancer allele present but no cancer no information Discuss the extent to which provides evidence that a faulty BRCA2 allele increases the risk of a person developing cancer. People whose families are suspected of having a faulty BRCA2 allele may choose to be tested for its presence in their own genome. A company based in the USA sells a microarray containing DNA probes for 20 different alleles that are associated with an increased risk of cancer, including the faulty BRCA2 alleles. This microarray can be used in a medical facility or research laboratory to test blood samples for the presence of these alleles. Explain the meaning of the term genome. Suggest a type of cell from a blood sample that is suitable for testing for the presence of this allele and explain your choice. Outline how a microarray enables the detection of particular alleles. Suggest one advantage and one disadvantage of screening for faulty alleles of BRCA2 before any symptoms occur. advantage disadvantage
9700_s17_qp_42
THEORY
2017
Paper 4, Variant 2
View
One cause of the genetic disease severe combined immunodeficiency (SCID) is a mutation in the ADA gene. This mutation results in a deficiency of the enzyme adenosine deaminase (ADA). Although ADA is found throughout the body, it is especially active in lymphocytes. The absence of functional ADA causes the build-up of toxic metabolites that kill lymphocytes and damage organs. Babies are often diagnosed with SCID by six months old. Treatment can greatly improve the life expectancy of children with SCID. Some treatment options are available. • Enzyme replacement therapy with recombinant human ADA made by genetically modified (GM) Escherichia coli. Weekly intra-muscular injections are given. • Bone marrow transplant if a well-matched donor, such as a close relative, can be found. • Gene therapy. Suggest and explain why it may be more appropriate to use enzyme replacement therapy to treat SCID instead of a bone marrow transplant. Outline the procedure used for gene therapy treatment of a person with SCID. Suggest the social and ethical implications of gene therapy for SCID that need to be considered before treatment is carried out.
9700_s23_qp_43
THEORY
2023
Paper 4, Variant 3
View
Huntington’s disease is caused by a dominant allele of the gene that codes for the production of the huntingtin protein. This protein affects the development of many different tissues, including brain tissue. • The Huntington allele contains several repeats of the base sequence CAG, which codes for glutamine. • This results in a polyglutamine section in the synthesised protein. • A gene with more than 39 CAG repeats produces a protein that does not fold properly and does not function. • Symptoms of Huntington’s disease usually first appear between the ages of 30 and 45 years. • There is no treatment for the disease, which is progressive and always fatal. • Some people with between 27 and 35 CAG repeats do not develop the disease, but may still pass on the Huntington allele to their children, who may develop the disease as the number of repeats tends to increase when gametes are produced. The amino acid sequences on either side of the polyglutamine section of the huntingtin protein are not changed by the presence of the CAG repeats in the Huntington allele. Explain why this is so. With reference to the information given, explain why Huntington’s disease cannot be treated with gene therapy. Young people who have a parent with Huntington’s disease can choose to be screened for the presence of the Huntington allele. State the probability that a young person who has one parent with Huntington’s disease will inherit the Huntington allele. Suggest one advantage and one disadvantage of screening for Huntington’s disease before any symptoms occur. advantage disadvantage A couple, in which one partner has the Huntington allele, may choose to use IVF (in vitro fertilisation) to have a child. Any embryos obtained from the IVF procedure can be screened in the following way: • carry out an embryo biopsy • use PCR • test for the presence of the Huntington allele • only implant embryos that do not contain the Huntington allele. State what is meant by the term embryo biopsy. Explain why PCR is used in this procedure. Outline two social or ethical implications of screening embryos in this way.
9700_w17_qp_42
THEORY
2017
Paper 4, Variant 2
View
Lung epithelial cells have a thin layer of watery mucus on their surface. The normal allele of the CFTR gene codes for a transport protein that transports chloride ions out of epithelial cells. is a diagram of part of the cell surface membrane and the mucus layer of an epithelial cell with normal CFTR proteins. outside cell thin mucus layer cell surface membrane inside cell Cl – water Cystic fibrosis (CF) is a genetic disorder caused by having two recessive alleles of CFTR. In severe cases of CF, the transport proteins are not added to the cell surface membrane. This causes the mucus layer to be thick and sticky. Explain why the absence of CFTR proteins will cause the mucus layer to be thick and sticky. The probability of a baby having CF when both parents are heterozygous carriers for CF is 25%. It is possible to carry out prenatal screening to check for CF by using one of these tests: • amniocentesis, using cells from the amniotic fluid • chorionic villus sampling, using cells from the placenta. Both tests slightly increase the probability of the pregnancy failing . Outline the advantages of carrying out prenatal screening for CF. Embryos produced by IVF may be screened for genetic abnormalities: • to test for a specific genetic disease, such as cystic fibrosis • to check whether there is an abnormal number of chromosomes present. To improve the success of implantation and pregnancy, only embryos without any form of genetic abnormality are transferred to the woman’s uterus. A new double screening method was trialled where a single embryo biopsy was taken and used to test for a specific genetic disease and to check the number of chromosomes. In the trial, 1122 embryos were tested using this double screening method. In the trial, of the 1122 embryos tested: • 50.6% did not have a genetic disease • 27.5% did not have a genetic disease and did not have an abnormal number of chromosomes (normal embryos). Only normal embryos were transferred into the women. The percentage of embryo transfers that resulted in pregnancy was calculated. The results of the trial using double screening of a single biopsy were compared to the results of IVF procedures that used standard screening methods, as shown in Table 4.1. Table 4.1 IVF method percentage of embryo transfers that resulted in pregnancy IVF with standard screening IVF with double screening Using the data in Table 4.1, discuss the social and ethical considerations of double screening for cystic fibrosis and chromosomal abnormalities in a single biopsy.
9700_s20_qp_43
THEORY
2020
Paper 4, Variant 3
View
Questions Discovered
107