An essential part of an organism is something that the organism cannot continue to be alive or reproduce without. For instance, mitochondria are essential to most eukaryotic cells. Genes can also be considered with regards to their essentiality. Essentiality is an important property in the context of pathogens, since drugs acting on specific genes that are not essential are less likely to be an effective treatment than those that are. In contrast, genes that are essential are in general thought to be better drug targets.
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Essential (biology) Wikipedia(Text) CC BY-SA