Explain antibiotic resistance in bacteria and its evolution.

Antibiotics are used as medicine to treat bacterial diseases. Bacterial diseases are the result of populations of bacteria, and bacteria within these populations are not all equally susceptible to antibiotics. This means some bacteria are more resistant to antibiotics than others, this resistance is caused by random gene mutations in the bacteria's DNA. Natural selection tends to favour bacteria that is more resistant: bacteria that are antibiotic resistant are far more likely to survive, reproduce and pass on the antibiotic resistance gene to their offspring thus increasing the antibiotic-resistance allele frequency within the population. The more antibiotics are used, the more resistant bacteria become due to this, this is the reason antibiotics should be used and prescribed with care by doctors and vets.