The PDx1 protein is found in a wide range of animal species where it is regarded as essential for normal metabolism. In sand rats, the gene coding for the PDx1 protein has a much lower proportion of A and T nucleotides than PDx1 genes from other animals.

Finding the complete DNA sequence of the PDx1 gene in sand rats has been difficult.
Sequencing involves splitting off nucleotides one at a time from single-stranded DNA.

What could account for the difficulty in finding the DNA sequence of the PDx1 gene in sand rats?

1. The PDx1 gene is present in only a small proportion of nuclei.

2. The PDx1 gene is transcribed in only some cells.

3. The strength of the hydrogen bonding between the two strands of the PDx1 gene is unusually high.