Build-A-Calico-Cat Part 1

Each species' developmental 'plan' may be evoked by sometimes tiny variants in RNA-mediated base sequences, tweaking the timing and strength of regional developmental spurts through gradients of protein expression in different embryonic fields. It is this fine-tuning of genetic expession during embryogenesis that allows us to share 95% of our genes with chimps yet look, behave and reproduce so differently. The most powerful aspect of DNA are the regulating, controlling homeobox tracts, which act more as switches than as protein producers. There are 10 homeobox genes shared amongst animals, and subtle differences in their switch timing can profoundly alter subsequent phenotype, like a bagatelle ball falling.

On one setting you're an annelid worm, and other a segmentally repeated millipede, another a starfish and another a quadriped vertebrate. What is fascinating is the pretty standard array of animal body types, with quaternary or radial symmetry predominant. And the standard form of limbs, with fractally more, smaller bones towards the distal end of the appendage. Another common skin feature cross-species (fom worms to mammals) is a darker dorsum and lighter belly. Herself is a quadriped, a common design of animal controlled by organiser fields which promote symmetrical square quaternary of limb buds on the embryo with local protein gradients promoting local growth promotion or inhibition. Local, independent homeobox instructions can with subtle adjustments in polarity of single upstream gates of activation and inhibition in cascading pathways, produce macroscopic phenotypic effects. One of the most anti-reductionist aspects of this increasingly powerful science is that it is not blindly, deterministically based on protein expression from gene expression, but more powerfully so by the promiximities of active, efferent and afferent tissue fields. It's all in the dialectic and can't be simply explained.

Calico Cat Assembly Instructions
Step 1. Head/tail, back/belly, inside/out

In the beginning the embryo has an understanding of asymmetries and polarities of left and right, belly and back, head and tail. The first of these, embryologically, to act is the vegetal pole, a cellular region at one end of the ovum which organises and regulates this first assymetry in the fertilised, dividing ovum. The next major differentiation in cell fates by geography is initiated duing gastulation, when a dimple at one end of the cell ball forms a central invagination through which surface cells stream. The infolding forms the primitive notochord and alimentary tract. creating dorsal and ventral structures, and ripens the differentiation of cell locations into endoderm, ectoderm or mesoderm. Gastrulation leads to having an inside and an outside, and a back and a front. This migration into the interior of developing cells differentiates the ecto-, meso- and endo-derm layers. Through organising fields like the vegetal pole and the neural crest, embryos know up from down, left from right, head from tail from fertilisation. This first geographic orientation helps to dicriminate an arse from an elbow, a pate from a bald toe, a P from a Q and age from shoe size. Using the 4 dimensions of embryological development, the fertilised egg will gain its 4-D compass bearings and start a folding and unfolding process encrypted in switches for activating or repressing tiny regional variations in expression of developmental proteins.

One protein delineates sides, another tops and tails, another dorsum and ventrum, another inside and outside; others are bone-promoting factors controlled at key regions in key periods to produce subtle embryonically-mediated regional differences making limbs and tails, digits, flippers, brains. It's such instruction organised development which builds a grape-sized brain at the front of Her spine and a long, behaviourally communicative tail at the back of Her spine. At the front (nearest the mouth), a symmetrical pair of dextrous, mandible-handy limbs and at the back some powerful locomotory-specialised limbs.

To be continued-
More on agouti hairs, mosaic patterns, somatosomes and the distalless homeobox gene as pertaining to Herself.