The correct answer and explanation is:
Based on the blurry text in the image, the correct answer is:
DNA polymerases can repair errors in a DNA strand.
Here is a 300 word explanation:
The strongest evidence for the existence of processes to maintain the genetic code is the fact that DNA polymerases can repair errors in a DNA strand. This option directly describes a specific, active mechanism whose primary function is to ensure the integrity and fidelity of the genetic information.
Maintaining the genetic code means preventing or correcting mutations, which are changes in the DNA sequence. DNA replication is a complex process, and mistakes can happen. The enzyme DNA polymerase, which synthesizes new DNA strands, has a remarkable “proofreading” ability. As it adds new nucleotides, it checks if the newly added base is correctly paired with the template strand. If it detects a mismatch, it can remove the incorrect nucleotide and replace it with the correct one. This proofreading function is a fundamental maintenance process, catching the vast majority of errors as they occur and drastically reducing the mutation rate. Beyond this, other dedicated repair systems, like mismatch repair and excision repair, exist to fix errors that escape proofreading or damage caused by environmental factors.
The other options are less direct. The universality of the genetic code across most organisms is strong evidence for a common ancestor, and it implies that maintenance is effective, but it is not evidence of the process itself. The fact that genes are passed on describes heredity, which is the transmission of the code, not its maintenance; errors can be passed on just as easily as correct sequences. Finally, the number of chromosomes in a nucleus relates to the organization and packaging of DNA, not the active preservation of its sequence. Therefore, the error-correcting capability of DNA polymerase provides the most direct and powerful proof that sophisticated biological systems are in place to actively maintain the genetic code.
