Homeosis

The formation of a normal plant or animal body structure or organ in place of another at an abnormal site. Examples of homeosis (also called homeotic transformation) are most obvious in insect appendages, where an appendage that is characteristic of one segment, for example the antennae on an insect head segment, are transformed into insect legs that normally develop only on trunk segments. Similar examples of homeotic transformations can also occasionally be found in vertebrates where lumbar vertebrae are transformed into thoracic vertebrae which then extend into rib processes, or in floral organs where petals are transformed into sepals. Homeotic transformations rarely occur in nature in living organisms, and are due to genetic defects in a class of proteins called homeotic proteins, the products of homeotic genes. Homeotic transformations may also be induced in the laboratory by the accidental or deliberate manipulation of homeotic gene expression so that homeotic proteins are produced in the wrong place or at the wrong time in developing plants and animals. See also Cell differentiation; Developmental biology; Developmental genetics; Gene action; Mutation.

Homeosis is the transformation of one body part into another, arising from mutation in or misexpression of specific developmentally critical genes. It may be caused by mutations in Hox genes, found in animals, or others such as the MADS-box family in plants. Homeosis is a characteristic that has helped insects become as successful and diverse as they are.^[1]

Homeotic mutations work by changing segment identity during development. For example, the Ultrabithorax genotype gives a phenotype wherein metathoracic and first abdominal segments become mesothoracic segments.^[2] Another well-known example is Antennapedia: a loss-of-function allele causes legs to develop in the place of antennae.

In botany, Rolf Sattler has revised the concept of homeosis (replacement) by his emphasis of partial homeosis in addition to complete homeosis, which is commonly accepted ^[3].

References

1. ^ Lodish et al., 2003. Molecular Cell Biology, 5th Edition. W.H. Freeman and Company, New York.
2. ^ Nusslein-Volhard & Wieschaus, 1980. Mutations affecting segment number and polarity in Drosophila. Nature 287, pp. 795-801.
3. ^ Sattler, R. 1988. Homeosis in Plants. American Journal of Botany 75: 1606-1617

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