Zerknüllt is a gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

 in the Antennapedia

Antennapedia

Antennapedia is a HOM-C gene first discovered in Drosophila which controls the formation of legs during development. Loss-of-function mutations in the regulatory region of this gene result in the development of the second leg pair into ectopic antennae...

 complex of Drosophila

Drosophila

Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...

(fruit flies), where it operates very differently than homologous genes in other organisms.

Zerknüllt codes

Genetic code

The genetic code is the set of rules by which information encoded in genetic material is translated into proteins by living cells....

 for a homeoprotein that helps shape the fly's tissue during embryogenesis. In Drosophila, zerknüllt's expression is repressed by dorsal protein. This normally limits its expression to roughly the dorsal 40% of the embryo, where the concentration of dorsal protein is low. Zerknüllt's homologs are hox genes, common to a vast range of organisms evolutionarily very distant from Drosophila, even including mammals. Hox genes are activated by genetic regulation mechanisms that target each gene's effect much more narrowly: to just one segment of the developing embryo, corresponding to the gene's position in the chromosome sequence.

Zerknüllt is commonly abbreviated zen.