Articles

Morphogenetic Genes, Symmetric Variation, and the Production of Form in Drosophilia

By Anonymous

Many of the main areas of development of form in the vinegar fly, Drosophila, are now known. The main aspects of the production of form are controlled by very special genes. One part of the egg chamber, in its early stage, is divided into many nurse cells and the oocyte, or the unfertilized egg, is in the other part of the chamber. There is a cytoplasmic bridge by which the mRNA molecules cross over from the nurse cells into the area of the oocyte. Cellular organelles and proteins also make this journey from the nurse cell region to the oocyte. The mRNA molecules help to restrict the expression and spatial distribution of proteins (Gehring, 1998, p. 138). The head versus tail polarity of the egg and beginnings of the embryo are dependent on this distribution of mRNA in an asymmetrical fashion.

The distribution of mRNA is caused by signals in the mRNA and on the RNA-binding proteins that recognize such signals (Cost and Schedi, 2001, pp. 593-595). Mter about two or three days the Hox gene called Hedgehog plays an early role by stimulating the change of ovarian somatic cells into stem cells. Without hedgehog this cannot happen (Zhang and Kalderson, ZOO I, pp. 599-604.

The polarity of the oocyte is established as soon as some of the mRNA molecules are translated into proteins. Bicoid is one such protein which helps establish the head end. In fact, if you put this protein at both ends, two heads result. RNA bicoid together with RNA's of two genes called oskar and torso-like produce three pathways which give rise to four protein gradients that start subdividing the embryo (N usslein- Volhard, 1996, pp. 38-43). A gradient of another protein called dpp actively subdivides the dorsal ectoderm of the Drosophila embryo into two areas: amnioserosa and dorsal epidermis. The two proteins called short gastrulation and tolloid help to shape this gradient (Ashe and Levine, 1999, pp. 427-430.

The Hox gene Hedgehog helps to initiate the formation of eyes and limbs (Brown, 200 I, pp. 48-49). Dpp also is seen as crucial for Drosophila wing development (de Celis, Barrion and Kafatos, 1996, pp. 421-424.

The main aspects of development are clearly caused by proteins and these proteins remain stable because of the principle of symmetric variation (Brown, 1999, p. 200). Some changes in DNA chemical bases that ultimately code for amino acids resulting in the proteins will produce the same outcome, hence the term 'symmetric: Other DNA changes will field amino acids within the same chemical group to which the original amino acid belonged. If these remain, they can produce broader changes. The enzyme repair system, however, will repair most of the changes including many that would be adverse. For a review of how all this works, see Brown, 1989, pp.I8-19. Changes therefore, in these proteins, can bring about changes in form but such change is moderated by symmetric variation and is thus always kept within the kind. We will have far to go before we can express the same detailed understanding of most life forms that is possible now with Drosophila, but what we do know supports the belief that the Creator produces an animal's form by means of a series of marvelous developmental genes. In one such example of a recent work, the face of a bird was shown to be produced by the working together of the morphogenetic protein Noggin and a vitamin A derivative called retinoic acid (Lee, Fu, Hui and Richman, 2001, pp. 909-912). Retinoic acid is a nuclear receptor. Surely each creature is "fearfully and wonderfully made."

Acknowledgements
I thank Paul Stanton for computer typing, George Howe for constructive criticism, and Sharron Hotchkiss for manuscript preparation.

References
CRSQ; Creation Re.~earch Society Quarterly.
Ashe, H. L. and M. Levine. 1999. Local inhibition and long range enhancement of dpp signal transduction by sog. Nature 398:427-431.
Brown, C. 1989. A mathematical illustration of the law of symmetric variation. CRSQ 26:18-19.
_____. 1999. The principle symmetric variation as it relates to silent mutations. CRSQ 36: 1 00.
_____. 2001. The production of form, Hox genes, and symmetric variation. CRSQ 38:48-49.
Costa, A. and P. Schedi. 200 I. Conservation signals location. Nature 381:593-595.
De Celis, J. F., E Barrio, and F. C. Katatos. 1996. A gene complex acting downstream of dpp in Drosophila wing morpho…

Creation Research Quarterly Volume 40, March 2004