June 09
2 Cystic fibrosis is a genetic disorder caused by one of a number of possible gene mutations. Prenatal testing can be used to determine whether or not a fetus has cystic fibrosis.
(a) Name one method of prenatal testing and explain how it can be used to detect cystic fibrosis. (3)
EITHER
1. amniocentesis ;
2. amniotic fluid removed (from amniotic sac of mother) / eq ;
3. {fetal / embryonic} cells present in amniotic fluid /{fetal / embryonic} cells needed ;
4. DNA can be analysed / eq ;
5. to detect {defective / eq} gene(s) (in sample) / eq ; OR
1. chorionic villus sampling ;
2. placental tissue removed (from womb of mother) / eq ;
3. fetal cells present in {placenta / placental tissue / chorionic tissue} / fetal cells needed ;
4. DNA can be analysed / eq ;
5. to detect {defective / eq} gene(s) (in sample) / eq ;
(b) Describe one benefit and one risk, to a pregnant woman, of prenatal testing. (4)
Benefit:
1. gives information about abnormalities (in Fetus) / eq ;
2. {opportunity for choice / eq} / {consider termination / eq} / time for {preparation / treatment / eq } / {peace of mind / eq} ;
Risk:
3. possibility of miscarriage (due to procedure) / eq ;
4. {potentially a healthy baby would be lost / eq} / {risk to mother / eq} ; OR
3. idea of {false positive / false negative} result ;
4. wrong decision made / description of wrong decision ; OR
3. {damage / harm} to fetus ;
4. subsequent health issues / miscarriages / eq ;
(c) Discuss either one ethical issue or one social issue relating to the use of prenatal testing. (2)
1. idea that a fetus is living ;
2. abortion is {wrong / murder} / eq ; OR
OR
1. issues relating to confidentiality of {parents / child} / eq ;
2. idea that {some other abnormality may be found / paternal DNA does not match / other family members have right to know results} ;
OR
1. that or some other abnormality may be found ;
2. comment on possible problems with {future employment / insurance / what constitutes a serious condition} / eq ;
OR
1. not fully understanding possible risks of prenatal testing; 2. possibility of {miscarriage / harm to child} / eq;
OR
1. {who has the right to make the decision for the fetus / fetus has decision rights} (if the test is positive) ;
2. {denying them the opportunity to live / fetus should be allowed to live / fetus has a right to live} ;
7ai) (a) (i) Distinguish between the terms allele and gene. (ii) Explain the meaning of the term recessive allele.
b) (i) Naveeda is homozygous. Explain the meaning of the term homozygous. (ii) Susan is also homozygous. Name the members of this family who are definitely carriers of albinism, giving reasons for your answer.
(c) Albinism occurs in a number of different animals, including squirrels as shown in the photograph below. The incidence of albinism in squirrels is 1 in 100 000 births, which is much lower than the incidence of albinism in humans. Suggest why the incidence of albinism in squirrels is lower than the incidence in humans, giving a reason for your answer. (2)
(d) Individuals with albinism are unable to produce the pigment melanin. This can be due to the absence of the enzyme tyrosinase. The diagram below shows the role of tyrosinase in melanin production. Tyrosine tyrosinase
dihydroxyphenylalanine Melanin. Explain why melanin cannot be produced in the absence of the enzyme tyrosinase. (2)
Jan10 – get ms
7. (b). Explain why it is necessary to test for several different recessive alleles in the screening for cystic fibrosis. (2)
1. cystic fibrosis results from one of a number of possible mutations (of this gene) /eq ;
2. idea that testing for only one will miss other recessive alleles ;
1. ref to false negatives / eq ;
2. idea that the screening programme does not test for all the possible mutations that can cause cystic fibrosis ;
3. idea that a mutation may occur in the formation of the gametes ; 4. idea of mutation in both gametes ;
5. idea that a mutation may occur after fertilisation ;
(d) In the risk analysis shown, if one of the partners is found to be a carrier then screening for cystic fibrosis may be offered to other family members. Explain why this screening is offered to other family members. (2)
1. idea that any other family member could be a carrier ;
2. idea that informed choices can be made about having children (if they know that they are carriers) ;
(e)Using your knowledge of monohybrid crosses, calculate the probability of having a child with cystic fibrosis if both partners are found to be carriers. Draw a genetic diagram to explain how you calculated this probability. (5)
1. heterozygous genotype of both parents shown or stated ;
2. possible alleles carried in the gametes shown (can be shown in a Punnet square) ;
3. possible genotypes of offspring clearly shown (can be shown in a Punnet square) ;
4. corresponding phenotypes given ;
5. (probability of having child with cystic fibrosis is) 25% / 1 in 4 / ¼ / 0.25 / ; Jan 11
5. Thalassaemia is the name of a group of inherited blood disorders that affect the body’s ability to produce haemoglobin in red blood cells. Red blood cells are produced in bone marrow.
Oxygen in the lungs binds to haemoglobin and is carried to the cells of the body to be used in respiration.
Beta thalassaemia is the result of a mutation in the gene coding for the β chain of haemoglobin. If a person inherits gene mutations from both parents, this person will show symptoms of anaemia and will require blood transfusions. Symptoms of anaemia include tiredness and breathlessness.
*(a) Using the information given above and your knowledge of gene mutation, suggest why a person with beta thalassaemia has symptoms of anaemia. (4) (QWC – Spelling of technical terms (shown in italics) must be correct and the answer must be organised in a logical sequence)
1. idea of (mutation/named mutation) causing different base sequence ; 2. reference to different {sequence of amino acids / primary structure} / eq ; 3. reference to {βchain/
4. haemoglobin no longer binds oxygen / binds less oxygen / eq ; 5. {less / no } oxygen {supplied / carried / eq} (to the cells) / eq ; 6. correct reference to respiration/eq;
7. Idea of breathlessness due to body trying to take in more oxygen ; 8. idea of tiredness due to lack of energy;
1. reference to use of{normal/correct}{allele / gene}; 2. for{haemoglobin/βchain};
3. reference to introduction of {gene/allele/ DNA} into cells ; 4. cells named as (bone)marrow/eq;
5. reference to use of vector (to introduce gene into cells) ; 6. (named vector) e.g. virus, liposome;
7. credit reference to appropriate mode of delivery of vector e.g. injection into (bone) marrow ;
8. reference to need for repeated treatment; Jan 12
5. Genetic screening can be used to determine if an embryo has a genetic disorder, such as cystic fibrosis.
(a) The table below refers to the methods used in preimplantation genetic
diagnosis and prenatal genetic screening. If the statement is correct, place a tick in the appropriate box and if the statement is incorrect, place a cross in the appropriate box. (2)
(b) (i) Name one method of prenatal genetic screening. (1)
amniocentesis / chorionic villus sampling / CVS ;
(ii) Discuss either one ethical issue or one social issue relating to the use of this method of prenatal genetic screening. (2)
1. idea of right to life ;
2. abortion is murder / ref to risk of miscarriage / eq ;
Or:
3. false positive / negative / eq ;
4. consequences of false result e.g. abortion of (healthy) fetus ; Or:
5. who has right to decide if tests should be performed / eq ;
6. {implications of medical costs / discrepancies over next step} / parents {have a right to know / can prepare / eq} ;
Or:
7. issues relating to confidentiality of {parents / child} / eq ;
8. idea that {some other abnormality may be found / paternal DNA does NOT match / other family members have right to know results} ;
Or:
9. if abnormality found / eq ;
10.consequence of abnormality found e.g. abortion, Or:
comment on possible problems with {future employment / insurance / what constitutes a serious condition} / eq ;
14. consequences of stress e.g. increased risk of miscarriage ;
(c) Gene therapy has the potential to treat some genetic disorders. (i)
Explain why gene therapy has the potential to treat some genetic disorders. (2)
(ii) Suggest how patients with cystic fibrosis could be treated using gene therapy. (3)
Jan13
8. Cystic fibrosis and albinism are examples of recessive genetic disorders. Tay-Sachs disease is another example of a recessive genetic disorder. (a) Explain the meaning of the term recessive genetic disorder. (2)
1. (the disorder results from a) defect in genes / eq ;
2. both (defective) alleles need to be present / homozygous / not expressed in the presence of a dominant allele / eq ;
*(c) Tay-Sachs disease is caused by a gene mutation that results in the build up of lipid in the brain. It is hoped that gene therapy will be able to treat this disease in the future.
Sheep can also suffer from Tay-Sachs disease. Investigations have found that gene therapy increases the life span of these animals.
Suggest how these gene therapy investigations could have been carried out. (5)
(QWC– Spelling of technical terms must be correct and the answer must be organised in a logical sequence)
1. {isolation / identification / eq} of normal gene / eq ; 2. {inserted / eq} into vector / stem cells / eq ;
3. vector named as {liposome / virus} ;
4. injection of {vector / modified stem cells} into {blood / brain / target cells / eq} / eq ;
5. ref to use of control injection ;
6. further detail of control injection e.g. use empty liposome / virus without gene inserted ;
7. progression of disease monitored / eq ; 8. life spans recorded / eq ;
9. reference to appropriate
comparison with control eg untreated sheep ; 10.idea that treatment needs to be repeated; 11.idea of replication of investigation;
June10
5 Cystic fibrosis is a genetic disease that can affect many body systems, including the respiratory system.
*(a) Explain how a gene mutation causes a build up of mucus in the respiratory system of a person with cystic fibrosis. (5)
(QWC – Spelling of technical terms (shown in italics) must be correct and the answer must be organised in a logical sequence)
1. reference to CFTR{protein/channel}eq;
2. reference to a different {aminoacid/ sequence of amino acids / eq} (on defective CFTR protein) ;
3. reference to change in protein;
4. reference to role of protein in transporting chloride ions ;
6. reference to sodium ions moving in ;
7. water does not move out (of cells)/water moves in (to cells) /eq ; 8. by osmosis/eq;
9. mucus (on cell surface){is not diluted/ becomes thicker / becomes stickier} / eq ;
10. (thickened mucus) cannot be moved by {cilia / coughing} ; 5bi)
1. idea that mucus {traps/eq}{bacteria/ pathogens} ;
2. idea that {bacteria/mucuscontainingthe bacteria} cannot be removed (by cilia);
3. idea that mucus provides conditions for bacteria to {live / grow / develop / eq} ;
4. reference to antibodies not being effective; 5. reference to trauma caused by coughing;
6. idea that resident {phagocytes/ macrophages} cannot destroy bacteria ; 8b) Cancer can cause a lot of pain. Pain can be reduced by a chemical called endorphin that is made by cells in the brain and spinal cord. Endorphin reduces the activity of neurones that carry impulses from pain receptors.
Gene therapy has been used in rats to increase the tolerance to pain. Viruses, containing a gene coding for endorphin, were developed. These viruses were injected into the spinal cords of a group of rats. The level of tolerance to pain was tested in these rats and in the rats in a control group.
(i) Describe the role of the viruses in this investigation. (2) 1. reference to (virus acting as a)vector;
2. idea that virus is used to get the {gene/DNA} into the cells ; June 11
3 Cystic fibrosis is a genetic disease that can affect many body systems, including the digestive system. In a carrier of this disorder, preimplantation genetic diagnosis can be used to detect the presence of an allele for cystic fibrosis.
*(a) Explain how cystic fibrosis affects the digestive system. (4)
(QWC – Spelling of technical terms must be correct and the answer must be organised in a logical sequence)
1. reference to CFTR {gene/channel}not functioning properly ; 2. reference to {thicker/stickier/eq} mucus ;
3. (mucus) blocks (pancreatic) {duct(s) / eq } ; 4. in the pancreas;
5. idea that enzymes cannot {be secreted into / reach} small intestine ; 6. idea of reduced digestion of {food/ named food} ;
7. reference to reduced absorption/eq; 8. idea of{malnutrition/weight loss};
9. idea of {self-digestion of(pancreatic)cells / problems controlling blood sugar levels / cysts / fibroids} ;
(b) Explain how preimplantation genetic diagnosis is performed to detect cystic fibrosis. (3)
1. reference to {IVF/description of preimplantation} ; 2. {embryo / eq} DNA analysed / eq ;
3. presence of CFTR {gene mutation/faulty allele / eq} tested for / eq ;
Any of the following paired points
1. who has right to decide if tests should be performed / eq ;
2. {implications of medical costs/disagreements over next step / embryo has rights} ;
OR
3. issues relating to confidentiality of{parents/ child} / eq ;
4. idea that {some other abnormality may be found / paternal DNA does not match / other family members have right to know results} ;
OR
5. idea some other abnormality maybefound/ false negative ;
6. comment on possible problems with e.g.future employment / insurance / what constitutes a serious condition / eq ;
OR
7. idea that embryo could be{damaged/ destroyed / discarded / eq} / false positive ;
8. embryo {is a potential life/has rights} /destroying embryo is {wrong / unethical / murder / eq} ;
June 12
8 Cystic fibrosis and albinism are examples of recessive genetic disorders. Krabbe disease is another example of a recessive genetic disorder. Krabbe disease is caused by mutations in the GALC gene, resulting in a deficiency of an enzyme called galactocerebrosidase.
(a) Explain the meaning of each of the following terms: (i) Mutation (2)
1. reference to alteration in DNA ;
2. change in {base (sequence) / quantity of DNA} / eq ; Recessive (1)
idea that both of these alleles need to be present in order for the recessive phenotype to be expressed ;
(b) Suggest how a mutation in the GALC gene could result in a change in the enzyme galactocerebrosidase. (3)
1. idea of a gene being a sequence of bases that code for the sequence of amino acids in the {protein / polypeptide chain /enzyme / galactocerebrosidase} ; 2. (gene) mutation will alter {DNA triplet / DNA code / codon / eq} / eq ;
3. this may result in a different {amino acid / stop codon / amino acid sequence / primary structure / eq} / eq ;
4. idea that this may change the {shape / eq} of {protein / enzyme} ; 5. therefore causing {no synthesis / incomplete / eq} of {enzyme / galactocerebrosidase} / change of active site / eq ;
(e) State how these parents could determine whether or not their unborn child has Krabbe disease. (1)
