Final answer:
Mutations that affect a single gene generally occur during the formation of gametes through the process of meiosis. These changes can be heritable germline mutations or non-heritable somatic mutations and may lead to genetic disorders or diseases like cancer.
Step-by-step explanation:
Generally, mutations that affect a single gene occur during the formation of gametes (sperm or egg cells), a process known as meiosis. In this context, germline mutations are heritable and will be present in every cell of the offspring.
These can result in various genetic disorders if they affect genes negatively. Point mutations, deletions, and insertions that occur in the DNA during cell division can change one or a few nucleotides. Environmental factors such as radiation, viruses, and toxic chemicals can also cause mutations.
Some mutations may occur in somatic cells, which do not give rise to gametes, and as a result, these changes are not passed on to the next generation. However, they can result in issues like the uncontrolled cell division seen in cancer. In contrast, germline mutations occur in cells that become sperm and eggs, affecting the individual's descendants.