Genetic markers have also been used to measure the genomic response to selection in livestock. Natural and artificial selection leads to a change in the genetic makeup of the cell. The presence of different alleles due to a distorted segregation at the genetic markers is indicative of the difference between selected and non-selected livestock.<ref>Rayaa, G. et al. 2002. The Use of Genetic Markers to Measure Genomic Response to Selection in Livestock. Genetics. 162: 1381-1388</ref>
Genetic markers also play a role in [[genetic engineering]], as they can be used to produce normal, functioning proteins to replace defective ones. The damaged or faulty section of DNA is removed and replaced with the identical, but functioning, gene sequence from another source.
This is done by removal of the faulty section of DNA and its replacement with the functioning gene from another source, usually a human donor. These gene sections are placed in solution with bacterial cells, a small number of which take up the genetic material and reproduce the new DNA sequence. Engineers need to know which bacteria have been successful in duplicating these genes so another gene is added, altering the bacteria's resistance to antibiotics. [[Replica plating]] or a fermenter is used to grow enough bacteria to test resistance to antibiotics. It is important that the cultures are not mixed.