Mistakes during mitosis lead to the production of daughter cells with too many or too few chromosomes, a feature known as aneuploidy. In addition to alterations in chromosome number, tumor cells show frequent structural alterations in chromosomes that include deletions, amplifications, and translocations.

A mutation is a change in the nucleotide sequence of the DNA in a cell. There are many different kinds of mutations. Mutations can occur before, during, and after mitosis and meiosis.

A mutation is a change that occurs in our DNA sequence, either due to mistakes when the DNA is copied or as the result of environmental factors such as UV light and cigarette smoke. Over a lifetime our DNA? can undergo changes or ‘mutations?’ in the sequence of bases?, A, C, G and T.

Mutation rate is calculated from the equation μ = m/N, where N is the average number of cells per culture (approximately equal to the number of cell divisions per culture since the initial inoculum is much smaller than N).

RNA viruses have high mutation rates—up to a million times higher than their hosts—and these high rates are correlated with enhanced virulence and evolvability, traits considered beneficial for viruses.

In the simplest situation with multiple concurrent beneficial mutations, there are three important parameters: the population size, N, the beneficial mutation rate per individual per generation, Ub, and the fitness increase provided by each mutation, s.

Mutations can result from errors during DNA replication or induced by exposure to mutagens (like chemicals and radiation). Spontaneous mutations occur at a rate of 1 in 10^5 to 10^8 and contribute to random population variation.

Antibiotic resistance is a consequence of evolution via natural selection. The antibiotic action is an environmental pressure; those bacteria which have a mutation allowing them to survive will live on to reproduce. They will then pass this trait to their offspring, which will be a fully resistant generation.

Bacteria reproduce rapidly, sometimes in as little as 20 minutes. Therefore, it does not take long for the antibiotic-resistant bacteria to comprise a large proportion of a bacterial population.

In summary, the 6 main causes of antibiotic resistance have been linked to:

• Over-prescription of antibiotics.
• Patients not finishing the entire antibiotic course.
• Overuse of antibiotics in livestock and fish farming.
• Poor infection control in health care settings.
• Poor hygiene and sanitation.

When bacteria become resistant, the original antibiotic can no longer kill them. These germs can grow and spread. They can cause infections that are hard to treat. Sometimes they can even spread the resistance to other bacteria that they meet.

Antibiotic resistance is accelerated by the misuse and overuse of antibiotics, as well as poor infection prevention and control. Steps can be taken at all levels of society to reduce the impact and limit the spread of resistance.