| Transgene | Cloned genes being introduced into host (usually eukaryotic). |
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| Transgenic Organism | Organism receiving transgene. |
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| Ectopic insertions | When transgenes are inserted randomly into genome. |
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| Targeted Insertion | Targeted insertion (aka gene targeting) is when an inserted transgene replaces homologous sequence on genome. |
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| Retroviruses | Advantages: integrates genes into host chromosomes, offering chance for long-term stability. Drawbacks: genes integrate randomly so might disrupt host genes; may infect only dividing cells. |
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| Adenoviruses | Advantages: Most do not cause serious disease; large capacity for foreign genes. Drawbacks: genes may function transiently, owing to lack of integration or to attack by the immune system. |
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| Adeno-associated viruses | Advantages: Integrate genes into host chromosomes; cause no known human diseases. Drawback: Small capacity for foreign genes. |
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