Biology 9700 · AS & A Level · Genetic technology applied to medicine
Genetic technology applied to medicine — practice question
Lung epithelial cells possess a thin watery mucus coating on their surface. The normal allele of the *CFTR* gene encodes a transport protein that moves chloride ions out of epithelial cells. Fig. 4.1 shows part of the cell surface membrane together with the mucus layer of an epithelial cell that contains normal CFTR proteins. Cystic fibrosis (CF) is a genetic disorder caused by possession of two recessive alleles of *CFTR*. In severe CF, the transport proteins are not inserted into the cell surface membrane. As a result, the mucus layer becomes thick and sticky.
(a)[2]
Explain why the lack of CFTR proteins will make the mucus layer thick and sticky.
(b)[3]
The probability that a baby will have CF when both parents are heterozygous carriers for CF is $25\%$. Prenatal screening can be used to check for CF by using one of these tests: amniocentesis, which uses cells from the amniotic fluid; chorionic villus sampling, which uses cells from the placenta. Both tests slightly raise the chance that the pregnancy will fail (miscarriage). Outline the advantages of carrying out prenatal screening for CF.
(c)[3]
Using the data in Table 4.1, discuss the social and ethical implications of double screening for cystic fibrosis and chromosomal abnormalities in one biopsy.
Worked solution & mark scheme
This 8-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Cl^- ions do not exit epithelial cells” …