Variation and adaptation (CCEA)Natural selection: antibiotic resistance
Organisms of the same species vary in many ways. There are two types of variation – continuous and discontinuous. Natural selection explains how evolution occurs.
There is variation within bacterial phenotypeThe visible characteristics of an organism which occur as a result of its genes.. Some are resistant to antibioticsSubstances that control the spread of bacteria in the body by killing them or stopping them reproducing. and some are not.
Treating bacteria with antibiotics provides competition.
The resistant individuals survive and the non-resistant individuals do not survive – this is differential survival.
The resistant bacteria are able to reproduce.
The resistant bacteria pass on the resistance gene to the next generation.
Resistant bacteria increase and non-resistant bacteria decrease in number.
The gene for antibiotic resistance is usually caused by a beneficial mutationA random and spontaneous change in the structure of a gene, chromosome or number of chromosomes. in the bacterial cells.