Mutations in the CFTR gene cause cystic fibrosis (CF). The non-mutated allele of the gene can be obtained and then introduced into the lung cells of a person with CF using liposomes as a vector. This treatment gives only short-term relief from the symptoms of CF.
Which of the following statements would be a correct explanation of this treatment?
Genes are unstable and break down over time in the cell.
Lung cells are constantly being replaced and new cells will have the faulty allele.
The non-mutated allele is recessive.
A. 1 and 2 only
B. 1 only
C. 2 only
D. 1 and 3 only
E. 2 and 3 only
This question is difficult due to the wording of the answers, they are just unclear and are not common statements made in the textbook. We just need to think about them logically:
1. Genes are unstable and break down over time in the cell.
Think about how complicated and delicate the DNA replication mechanisms are, does it really make sense that something so precise could result in instability? This is purely using logic, if we look at the actual structure of DNA, what is carrying genes, then we can see identify things like phosphodiester bonds and other things such as hydrogen bonding within the DNA molecules. Genes do not break down over time, rather the cells are replaced over time as they age (dependent). Therefore 1 cannot be correct.
2. Lung cells are constantly being replaced and new cells will have the faulty allele.
As we said earlier, the genes are not broken down over time, rather the cells are replaced, and as a result, there is fresh DNA. Unless you can change the DNA of the cells that are dividing to make it so new daughter cells are containing these healthy alleles, then the original lung cells with the faulty alleles will continue to divide. Therefore 2 is correct.
3. The non-mutated allele is recessive.
It does not matter whether the non-mutated allele is recessive or not. The problem is that we have no way of permanently changing the genetic information of all lung cells in order to maintain these normal unaffected cells. Therefore 3 is also incorrect.
\fcolorbox{red}{grey!30}{As we can see, C is the correct answer.}