PasoVoice.Com :: GENETICS!

caliber · Site Admin

Richard D. Squire, PhD (Genetics)
Professor of Biology
University of Puerto Rico, Mayaguez Campus

The Puerto Rican Paso Fino is the unique product of a selective breeding program within a primarily closed population. The current Paso Fino gene pool (genetic make up of the population) is thus distinctly different from all other current breeds, including its own ancestral strains. The physical characteristics, disposition and temperament, and style and performance are the sum product of many different pairs of genes interacting with each other to form the genetic background which yields the Paso Fino of today. The expressions of the major genes (which have the greatest effects on these characteristics) are modified by their genetic background, they are not completely independent of the other genes of the organisms. This is why selective breeding continues to improve a strain over generations, even after the main characteristics are set. Selection for the best (most harmonious, or enhancing) modifier genes improves the final characteristics.

Any large scale uncontrolled infusion of "foreign" genes into the pure bred Paso Fino gene pool (Registry A) would in all probability undo years of careful breeding, because it would break up the necessary genetic background and adulterate it with genes which are unsuitable due to their inability to act harmoniously with the Paso Fino gene combinations. Such a contamination of the Paso Fino gene pool might be impossible to correct unless all horses of "contaminated" (outbred) ancestry were then removed from Registry A. Such a loss could seriously reduce the size of this registry and therefore reduce the amount of desirable genetic variation within the Paso Fino Registry A population. Such a reduction in genetic variation could seriously limit the further improvement of breed characteristics by selection for the best gene combinations within the Paso Fino genetic background.

All of this has direct bearing on the question of whether or not to permit the inclusion of the Paso Colombiano into the Paso Fino Registry A. Although both breeds were developed from early imports of horses by the Spanish, the genetic "mix" of the breeds varied in the imports which went to Puerto Rico, and then later to other sites in South America and California. The Paso Colombiano was developed independently from the Paso Fino of Puerto Rico. The gradual selective process which independently produced each of these two breeds must have incorporated different gene combinations over time. Uncontrolled large-scale crossing of the two breeds would therefore result in the destruction of both gene pools. The unique characteristics of each would be lost as special gene combinations were broken up. I should emphasize that apparent similarities or alleged similarities, in animal strains and even closely related species, are often the product of uniquely different gene combinations. Thus their apparent physical "identity" is an illusion. The uncontrolled merging of the Paso Fino of Puerto Rico with the Paso Colombiano is therefore a "disaster waiting to happen". Evidence of this is seen in the large amount of segregating variability of traits in the PRPF-PC F2 and later generation hybrids.

All of this should not be seen an attempt to dissuade all hybridizations between the two breeds, however. Carefully conducted crosses should be made in order to determine the genetic bases responsible for the characteristics of each breed. Selective breeding over many generations might in time produce a new "Paso Americano" with its own characteristics. Such a new "Paso" might even be superior in some ways to one or both of the "Pasos" of today. However, such hybrids and their descendents should be barred from both the Paso Fino and the Paso Colombiano registries. These uniquely valuable gene pools need to be protected from adulteration.

Richard D. Squire, Ph.D. (Genetics)
Professor of Biology
University of Puerto Rico, Mayaguez Campus
rickmart@coqui.net