The selfish gene theory postulates that natural selection will increase the frequency of those genes whose phenotypic effects ensure their successful replication. Generally, a gene achieves this goal by building, in cooperation with other genes, an organism capable of transmitting the gene to descendants. Intragenomic conflict arises when genes inside a genome are not transmitted by the same rules, or when a gene causes its own transmission to the detriment of the rest of the genome (this last kind of gene is usually called a selfish genetic element, ultraselfish gene, or parasitic DNA).