How can a mutation give an organism an advantage?

Answer 1

The most obvious example of the principle is found in the hospital closest to you. Hospitals need to be vary careful about the possibility of bacterial infection, since people admitted to hospitals often have weakened immune systems, and the possibility of infection during surgery is always there. Bacterial infections are often treated with anti-biotics, that target specific mechanisms and structures in the bacterium. Unfortunately, bacteria are continuously evolving, mutating, producing new variants. Mutation of the gene associated with the structure that is targeted by a specific anti-biotic can cause the bacterium to become immune to the anti-biotic, rendering it useless, and increasing the risk of infection for patients. This has lead to the evolution of MRSA - Methicillin- (or multiply) resistant Staphylococcus aureus, a bacterium that is insensitive to multiple types of antibioticum and a serious concern for hospitals.

Answer 2

A mutation that changes the protein coded by the gene in a way that changes its operation in a way that causes organisms having the mutation to survive and reproduce slightly more effectively than those organisms not having the mutation. This is the process of natural selection acting on variations produced by mutations.

Most mutations will fail and die out, but with quintillions of microorganisms undergoing billions of mutations every day, a few thousand mutations here and there will "succeed" and be passed on as "advantageous".

Large multicellular organisms tend to find mutations more troublesome than microorganisms do, so they have genetic repair and editing systems (that originally evolved in some microorganisms) that seek out mutations and remove them as well as having a small number of cells dedicated to reproduction while the rest of the body's cells can accumulate mutations without their affecting future generations (whether the mutations are advantageous or disadvantageous).

Some viruses (e.g. HIV) actually go the opposite way from multicellular organisms as more variations produced by mutations give them more chances to gain an "advantage" over the hosts they parasitize and have "sloppy replication" systems that make many mistakes and increase the number of mutations they have!

Answer 3

No. Many mutations can have adverse effects or no effect at all.