The Upright Ape: A New Origin of the Species

by Aaron G. Filler, MD, PhD

Figure 1-3 Antennapedia

Figure 1-3 – The Antennapedia Homeotic Mutant

An important source of the key breakthrough that has ultimately led to the deciphering of the genetic code that spells out the embryologic assembly instructions of most animals. This mutant fly has fully formed legs in place of antennas. It is a “homeotic” error mutant – a structure has been placed in the wrong body segment.

Further detail:

The Antp+ gene product is involved one of several mutations discovered in the 1970's that caused "atavistic" changes that tended to return complex advanced or specialized insect segmental anatomy into the simpler standard thoracic leg bearing segments of a "millipede-like" ancestral form. In 1981, Gary Struhl discovered a "null" mutant and thereby showed that the absence of the gene product resulted in the second thoracic segment leg being converted into an antenna. He also showed that the gene product could carry out its effects on segmental determination by diffusing throught the embryological tissues that it affected - hence it was a controlling signal rather than a being a "regional fate" for a given tissue. He also showed that this product affected multiple different types of tissues in the segment - such as the cuticle (outer shape of the segment) and the imaginal disk (the portion of the larva that forms into the adult appendage). This report created considerable excitement among geneticists who believed they would soon decode the genetic system that directed the assembly of embryos. The evidence that a homeotic gene product directed regional specialization help set the stage for understanding the meaning of the homeobox genes that were first discovered in several labs shortly after this paper was published.

Figure credit -

From: Griffiths, A. J. F. (2005). Introduction to Genetic Analysis. New York, W.H. Freeman.

Photograph by F. Rudolf Turner, Department of Biology, Indiana University, Bloomington and reproduced with his permission.

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