What is the primary cause of gene mutations?

The primary cause of gene mutations is linked to errors that may occur during DNA replication or the influence of mutagens. Mutations can arise naturally as DNA polymerases replicate the DNA strand—the enzymes responsible for copying DNA can occasionally incorporate incorrect nucleotides, leading to changes in the genetic sequence. These errors might remain uncorrected if the cellular repair mechanisms fail to identify and fix them.

Additionally, mutagens, which are physical or chemical agents that induce mutations, can also play a crucial role. For instance, exposure to radiation or certain chemicals can damage DNA and lead to alterations in the genetic code. Therefore, the correct answer emphasizes both the intrinsic errors associated with DNA replication and the extrinsic factors that can induce mutations, making it the most comprehensive explanation of the primary causes of gene mutations.

Considering the other options, while environmental factors can contribute to mutations, they do not encompass the full range of potential causes like DNA replication errors and mutagens. Similarly, normal cellular processes can include DNA replication, but they do not specifically address the mutation aspect. Lastly, interactions between different species pertain more to ecological and evolutionary concepts rather than the direct mechanisms that cause mutations in genes.