FIXING THE TYPE
by Loren Bolinger, 2/27/04 - 3/3/04, Monday, August 22, 2005
How the early breeders fixed the type of the Thoroughbred: Intermingled colateral matrilines,
and melded early Founder patrilines. How their stewardship of the breed was so successful that
today's horsemen are still reaping the rewards of their pioneering selective mating techniques.
The science of genetics has acknowledged and proved the validity of many of the early techniques.
The breeder manipulated the
genotype through selective mating techniques, typically inbreeding and
the recognition and repetition of certain pedigree patterns. The
breeder selected and culled though evaluation of the resulting
offspring of the mating primarily through phenotype measured by
objective performance and/or its relationship to performance.
Establishing the Typology
The Thoroughbred horse is a hybrid breed that normally does not breed
true-to-type. The racehorse breeder attempts to reduce the phenotypic
volatility or variability in the racehorse he breeds through employing
mating strategies that increase multiple instances of inbreeding or
linebreeding over successive generations, while culling out those
individuals that fail to meet expectations. Inbreeding reduces the
number of ancestors in a pedigree by duplicating those thought to be
more important or prepotent. By purifying the ancestry, the breeder
reduces the variability, hopefully to increase the probability of
breeding true-to-type.]
Fixing the type means to
reinforce a family’s or strain’s phenotype through
selective breeding, heavy overall inbreeding, and culling. The purpose
of fixing the type is to increase the permanence and stability of the
genotype so that the breeder can more reliably predict the phenotype
and to more reliably trigger the expression of performance traits in
the offspring resulting from selective matings. By increasing stability
of the genotype through careful reduction of the total number of
ancestors, variability of the phenotype can be dramatically reduced.
Selective breeding techniques have been devised that attempt to more
reliably predict and reproduce desired inherited traits and
characteristics in offspring from selective matings without
significantly increasing deleterious possible side effects of
inbreeding. Typology means the phenotypic or physical characteristics
that are manifested from an offspring’s genotype and the
environment with which it interacts.
How Fixing the Type was Acomplished
Selective mating was accomplished through three general strategies:
Genetic Isolation - Differentiation [breeding toward a desired goal]
cannot take place unless no new genetic material is introduced over a
period of time. No additional founder-type bloodlines were introduced,
once the original male and female Founder stock was chosen. Artificial
Selection - The breeder selects matings between individuals exhibiting
desired traits or attributes and avoids random matings. Inbreeding -
Inbreeding reduces diversity [weeds out undesirable traits] while
fixing or reinforcing desired traits. In order to “fix
type,” a breeder or several generations of breeders must closely
linebreed among the descendants of several, selected, prepotent
individuals that are complementary to each other and in whom a high
rate of successful offspring are produced. In this way, the breeder
concentrates the successful and productive genetic assets of a family.
The breeder selects patterns that sex-balance the immediate descendants
of duplicated ancestors, selects mates in such a way that patterns of
inversion in their bloodlines-in-common occurs along paternal and
maternal wings, inbreed to great mares and to great matrilines. The
breeder selects prepotent stallions from compatible bloodlines, and
avoids, as much as possible, excess male inbreeding while
simultaneously increasing inbreeding to females, and increases the
overall quality and quantity of matriarchs/great mares in the pedigrees
of the offspring. The above are some of the selective mating strategies
that lead to success. The final strategy, sometimes emotionally
difficult, is to cull for failure. Cull for failure to perform, cull
for deviation from phenotype. Selective mating means to select mates
based on the most reasonable hypotheses and objectives concerning
bloodlines, pedigree patterns, and phenotype. Those that fail to live
up to the objectives should be culled from the selective breeding
program.
Pedigree Matching
Bloodlines colateral to each other share an important role in the
selective mating technique called pedigree matching, that is, utilizing
those bloodlines that developed in parallel with one another. Pedigree
matching means that ancestors of the colateral bloodlines share kinship
or relatedness with one another through powerful ancestors-in-common.
The hooks of the key members of the colateral bloodlines were commonly
opposite-sex-balanced - ancestral links or hooks inverted by sex from
each other.
Loren Bolinger