Final answer:
The average number of mistakes in newly replicated DNA strands is extremely low due to DNA polymerases' proofreading and DNA mismatch repair systems which correct potential errors, resulting in an error rate of approximately 1 in 10 billion nucleotides.
Step-by-step explanation:
On average, the number of mistakes per newly replicated DNA strand is remarkably low due to the highly accurate nature of the DNA replication process. During replication, enzymes like DNA polymerase perform a critical proofreading function. This enzyme reads each newly added base to ensure it is complementary to the corresponding base on the template strand, correcting mistakes as they are identified. Furthermore, if mistakes do occur and are not immediately corrected by DNA polymerase, DNA mismatch repair mechanisms can often fix these errors, maintaining a high level of genomic integrity. These mechanisms are so effective that the error rate is about 1 in 10 billion nucleotides, or equivalently, fewer than one error per DNA molecule replicated.