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Pure Puerto Rican Paso Finos & Paso Colombianos - Two
Distinct Gene Pools
by
Richard D. Squire, Ph.D.
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.
published by permission of
Richard D. Squire, Ph.D. (Genetics)
Professor of Biology
University of Puerto Rico, Mayaguez Campus
rickmart@coqui.net
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