Final answer:
In biology, the probability that a mutation is fixed in a line each generation depends on several factors. Beneficial mutations are rare, but they play a crucial role in major evolutionary changes over time.
Step-by-step explanation:
In biology, the probability that a mutation is fixed in a line each generation depends on several factors. While most mutations are harmful, some can be beneficial. The chances of a beneficial mutation arising in a small population exposed to a new detrimental environmental condition are negligible. However, over the long term, major evolutionary changes depend on the introduction of new genetic characteristics through random mutation.