2.5.3 Uses of genetic screening and prenatal testing Quiz: Pearson Edexcel Biology A (Salters-Nuffield), Unit 2

The 20 questions

1. What is the purpose of carrier screening?

   • To identify people who carry one copy of a recessive allele and show no symptoms
   • To identify people who have already developed the symptoms of the condition
   • To cure a recessive condition by inserting a healthy copy of the gene
   • To measure the protein levels of an unborn child in the womb

2. What does pre-implantation genetic diagnosis (PGD) involve?

   • Testing a fetus in the uterus after implantation using a needle guided by ultrasound
   • Removing an egg from the ovary and testing it before fertilisation takes place
   • Screening a newborn's blood for a genetic disorder shortly after birth
   • Testing embryos created by IVF for a genetic condition before one is implanted in the uterus

3. Which fluid is sampled during amniocentesis?

   • Blood from the umbilical cord
   • Amniotic fluid surrounding the fetus
   • Cerebrospinal fluid from the fetal spine
   • Synovial fluid from the fetal joints

4. What tissue is sampled during chorionic villus sampling (CVS)?

   • The fetal liver, sampled through the abdominal wall
   • The uterine lining, which contains no fetal cells at all
   • The mother's bone marrow, which carries fetal DNA
   • Tissue from the placenta, which has the same genetic make-up as the fetus

5. Which prenatal test is usually performed earlier in pregnancy?

   • Chorionic villus sampling
   • Neither is performed before birth
   • Amniocentesis
   • Both are performed at exactly 40 weeks

6. Which statement about prenatal sampling procedures is correct?

   • Miscarriage risk applies only to pre-implantation genetic diagnosis
   • Only chorionic villus sampling carries a miscarriage risk, because it is invasive
   • Both amniocentesis and chorionic villus sampling carry a small risk of miscarriage
   • Neither procedure carries any risk to the pregnancy

7. Two carriers of a recessive condition use PGD. Which embryos would normally be selected for implantation?

   • Embryos that carry two dominant alleles at the locus
   • Embryos found to be unaffected, whether carriers or non-carriers
   • Only embryos found to be affected, so the condition can be studied
   • All embryos, regardless of their genotype, to maximise the number of pregnancies

8. Two carrier parents each produce three embryos by IVF. If each embryo independently has a 1/4 chance of being affected, what is the probability that none of the three embryos is affected?

   • 27/64
   • 1/4
   • 1/64
   • 9/64

9. Why might a prenatal test be offered to a couple who are both carriers of a recessive allele?

   • To determine the sex of the fetus, which is the main reason for the test
   • To determine whether the mother will be able to breastfeed the baby
   • To assess how many eggs were released during the menstrual cycle
   • To determine whether the fetus has inherited two copies of the recessive allele

10. A positive prenatal screening result is obtained for a serious inherited condition. What implication is most important?

    • It may raise difficult decisions for parents about whether to continue the pregnancy
    • It proves that the child will have severe symptoms throughout life
    • It removes the need for any medical care for the child after birth
    • It guarantees that the mother is a carrier of the same condition

11. A prenatal test reports that a fetus has two copies of the CF allele. Which outcome is expected?

    • The child will be healthy because the mutant alleles cancel each other out
    • The child is expected to develop CF, although the severity varies between individuals
    • The child will show CF only if the mother has the disease herself
    • The child will be a carrier with no symptoms throughout life

12. Two carrier parents have two children. What is the probability that at least one child is affected by a recessive condition?

    • 7/16
    • 9/16
    • 1/16
    • 1/4

13. Which screening test is commonly carried out on newborn babies in the UK for some inherited conditions?

    • A blood spot test taken from a heel prick
    • A urine test for glucose only
    • A biopsy of the spinal cord
    • A chest X-ray in the first hour after birth

14. Why can the result of amniocentesis take some time to become available?

    • The mother's blood must be filtered before the sample can be analysed
    • The results must be sent to a central national database before release
    • Fetal cells must be cultured in the laboratory before chromosomal or DNA analysis can be carried out
    • The fetus must grow to a larger size before the sample can be taken

15. What is a disadvantage of PGD compared with prenatal testing during pregnancy?

    • It requires IVF, which is costly and physically demanding for the couple
    • It can only identify conditions linked to the X chromosome
    • It always produces twins, which increases the risk to the mother
    • It is performed after the child is born, so decisions are delayed

16. What does a karyotype show?

    • The blood group of an individual
    • The sequence of amino acids in a protein
    • The number and structure of chromosomes in a cell
    • The rate of respiration in a cell

17. A woman is 11 weeks pregnant. Why might an earlier test such as CVS be an advantage?

    • Results are available sooner, which gives more time to consider options
    • The fetus is larger, so more DNA can be sampled from it
    • The amniotic fluid is more concentrated, which improves the accuracy of the test
    • The placenta is fully formed, so there is no risk of infection

18. In a population where q = 0.05 for a recessive allele, what percentage of people are carriers, approximately?

    • 5%
    • 9.5%
    • 95%
    • 0.25%

19. In PGD, why is a single cell usually removed from each embryo?

    • So that the sex of the embryo can be checked by visual inspection
    • So that its DNA can be analysed without seriously harming the developing embryo
    • So that the embryo is stimulated to undergo further cell division
    • So that a tissue culture can be grown from the embryo's blood

20. Which ethical concern is most directly raised when genetic screening results are shared with relatives without the individual's consent?

    • Confidentiality and informed consent
    • Equality of the sexes in competitive sport
    • The economic efficiency of the NHS
    • The right to vote in national elections

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