Which of the following can lead to alterations in gene regulation?

Viral insertion is a process where viral DNA integrates into the host genome, which can significantly impact gene regulation. When a virus inserts its genetic material into the DNA of a host organism, it may disrupt existing genes or regulatory elements, leading to changes in how genes are expressed. This can result in either the activation or repression of nearby genes, thereby altering the normal regulatory mechanisms in the host cell. Such alterations can have various biological consequences, including the potential for oncogenesis (cancer formation) if the inserted viral genes lead to aberrant cell proliferation.

In contrast, gene cloning primarily focuses on creating copies of a specific gene and does not inherently change gene regulation. DNA sequencing is a technique used to determine the sequence of nucleotides in a DNA molecule and does not actively alter gene regulation. Antiviral treatment is designed to target and inhibit viral replication and does not modify gene expression directly in the context of genetic alterations. Therefore, among the provided choices, viral insertion uniquely stands out as a method that can actively lead to changes in gene regulation.