Question

A group of scientists were using CRISPR to treat a mouse with cystic fibrosis, a disease caused by a defective CI-channel protein called CFTR. The most common cause of cystic fibrosis in humans is the absence of a phenylalanine, an amino acid, in the CFTR protein, which prevents CFTR from achieving the correct 3-D structure.

If the scientists wished to repair this mutation, how would they alter the mutated CFTR gene before using CRISPR to insert the DNA into the mice?

- Fix the frameshift mutation by removing thymine from the correct location in the CFTR gene.
- Fix the deletion mutation by inserting three adenines into the correct location in the CFTR gene.
- Fix the point mutation by inserting cysteine and removing an adenine from the correct location in the CFTR gene.
- Fix the inversion mutation by removing a fourteen-nucleotide stretch, turning it around, and then re-inserting it into the correct location in the CFTR gene.

Answer 1

To repair the mutation causing cystic fibrosis, scientists must insert three nucleotides back into the DNA sequence of the CFTR gene to restore the missing phenylalanine. This fixes the deletion mutation consistent with the disease's most common genetic cause.

Step-by-step explanation:

If the scientists wished to repair the mutation in the CFTR gene of a mouse with cystic fibrosis, they would need to address the specific type of mutation that results in the disease. The most common mutation causing cystic fibrosis is the deletion of a single amino acid, phenylalanine, which is due to a deletion of three nucleotides (triplet) in the DNA sequence of the CFTR gene. To correct this, they should:

• Fix the deletion mutation by inserting three nucleotides - specifically cytosine, thymine, and guanine (CTG) - into the correct location in the CFTR gene sequence. This would restore the missing phenylalanine in the CFTR protein and potentially correct the 3-D structure necessary for its function.

The other options such as fixing frameshift, point, or inversion mutations are not relevant in this context as they describe different types of genetic alterations that do not fit the known cause of cystic fibrosis.