Evaluate how genetic screening identifies alleles early, helping diagnosis, risk assessment and reproductive decisions while considering the evidence and limitations in Cambridge…
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.
Fig. 4.1 is a diagram of part of the cell surface membrane and the mucus layer of an epithelial cell with normal CFTR proteins.
Fig. 4.1
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.
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 (miscarriage).
Outline the advantages of carrying out prenatal screening for CF.