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THE AMERICAN SOCIETY OF ANIMAL PRODUCTION
GENETICS
IN PRACTICAL
STOCK B R E E D I N G
BY E. G. RITZMAN
New Hampshire Agricultural Experiment Station
The a r t of animal breeding has gone through a process of
slow evolution which is characterized by three distinct stages
of advancement. Since the earliest days of history mankind
has been t r y i n g to control in some measure or other the transmission of desirable Or undesirable physical characteristics or
functions. No other science has been more inviting to our innate
curiosity, b u t its history also shows that no other line of investigation has been more baffling. As a consequence a large p a r t of
the earlier work was based on general observation supplemented
by no small degree of speculative assumptions. The simple f a c t
that "like produces like" was one of the first of these general
observations and its general t r u i s m was so striking t h a t it has
held the stage since the early records of history. Practically all
the progress in animal improvement has been due to intelligent
application of this principle. As animal f o r m s and functions
were improved and artificially bolstered up it soon became
a p p a r e n t that the exceptions to the rule were quite common, but
it took y e a r s before it became recognized that the g e r m plasm
of an animal was not necessarily identical with its somatoplasm.
The first really marked scientific advance along this line was
b r o u g h t about by the Weisman and Darwin School of investigators in pointing out t h a t the carrier of h e r e d i t a r y qualities,
the germ plasm, represented an ancestral composite which did
not necessarily conform to the somatic expression of the carriers
of that germ plasm. On the basis of this new philosophy was
built the first a t t e m p t at scientific analysis and control of
h e r e d i t a r y influences. The means by which this was carried on
consisted in a mathematical analysis of the probability with
which an animal could t r a n s m i t his own physical characteristics
b y exact m e a s u r e m e n t of those t r a i t s together with those of his
ancestry. Galton's law of ancestral heredity was, therefore,
merely a modification of the original rule and, while it improved
the method o f analyzing the probable potential t r a n s m i t t i n g
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qualities of an animal, it still left the control of h e r e d i t a r y qualities dependent on a wide margin of chance. Mendel also began
essentially as a biometrician, but his unique method of attack
b r o u g h t forth the key to the situation by showing that h e r e d i t a r y
factors are unit characters capable of combining and segregating
in definite proportions.
Mendelism m a r k s the first step in the possibility of controlling the hereditary qualities of our domestic animals, but its
validity rests on the premise that the parent stock must be pure
with regard to the t r a i t under consideration. It is essentially
a process of selecting f r o m any source of parentage the characteristics desired to be united in the first cross or F1 generation.
This F1 is of course a crossbred c a r r y i n g gameticaUy all the
desirable as well as the undesirable traits of the two parents.
Its somatic development m a y be desirable or undesirable. In
fact, while animal breeders have often resorted to crossing on
the ground t h a t the first cross was physically superior, the
somatic development of the F1 is scientifically u n i m p o r t a n t since
it is highly heterozygous. The important function of the F1 is
that when inbred to itself it t u r n s out to be a P a n d o r a ' s box
from which all sorts of new combinations issue, some pure in
character and some mixed.
In our domestic livestock the term purebred is in a sense
very misleading. Since most of our pure breeds have been
built up f r o m a combination of blood, they are all relatively
heterozygous with regard to certain of their t r a i t s especially
those relating to conformation. Nevertheless, inbreeding tends
to intensify these traits so that the germ plasm will more nearly
represent the soma of its host. Now, remarkable as it m a y
seem, our improved breeds have unconsciously been produced
by Mendelism, the original improvers like Bakewell, Collins, and
others having possessed a high degree of intuition in selecting
the dominant individuals t h a t issued f r o m the P a n d o r a ' s box.
More recent achievements like the famous Corriedale are nothing
b u t the result of inbreeding hybrids, since it is a fact t h a t in
some of the most noted foundation flocks of this breed in N e w
Zealand no outside blood was used for periods involving six to
eight generations. While it has always been supposed that such
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THE AMERICAN SOCIETY OF ANIMAL PRODUCTION
intense inbreeding would finally be injurious, all the more noted
improvers of livestock seem to have been able to avoid such
misfortune by intelligently discarding the potentially harmful
inbred individuals. The guiding principle by which they determined the desirable from the undesirable was not given to
posterity. It was probably largely unexpressed intuition since
they were ignorant of the laws of dominance and recessiveness,
but it is more or less certain that the old school of improvers
deemed it essential that physical or somatic perfection involved
also a superior expression of character, suggestive of strength
in the male and feminine gentleness in the female.
Now the general history of improved breeds is much the
same; usually a mixture of quite unlike blood was used to furnish
that combination of traits which was desired, the next step
being usually inbreeding to maintain the standard, incidentally,
however, intensifying the germinal determiners. Then there
followed a general dissemination and demand for such improved
stock beyond the available supply, which of course resulted in
bringing in much new blood, curtailing selection and, therefore,
generally weakening the breed by establishment of a large number of subfamilies developed along different blood lines.
Practical breeders have not recognized sufficiently the
importance of concentrating along a chosen blood line to intensify t h e germinal determiners notwithstanding the fact that the
breeding of outstanding producers repeatedly illustrates this
point. Much of the more recent genetic investigations on the
breeding of show animals emphasizes the important part that
concentration of specific blood lines has played in producing
winners. This simply supplies the proof to the progress of breed
history in general that prepotent individuals can be produced
only by concentration of germinal factors representing similar
somatic or functional characteristics.
While genetics has thus already accomplished much of practical value in analyzing the causes that have produced successful
animals in the past, its chief effort and contribution is along
more basic lines of tying up the physical and functional traits
of animals with the influences or causes that bring about variation between individuals. Cytological research has 'already
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t h r o w n much light on the p a r t played by the chromosomes in
the transmission of h e r e d i t a r y qualities, a number of which,
such as color, horns, ear length, fecundity in poultry, etc., have
been assigned a definite genetic constitution controlled by presence or absence of a definite number or combination of genetic
factors t h a t conform to the law of segregation.
While the practical application of genetic factors or rules
by which the transmission of somatic t r a i t s can be controlled
thus apply for the most p a r t to traits which have no g r e a t economic significance, there is some evidence that functional traits
as well as conformation m a y eventually be correlated with t h e i r
tangible unit factors or d e t e r m i n e r s when the analysis of the
soma is made on the basis of skeletal units, that is, on single bone
dimensions. Since conformation as it is now treated in practice
is a complex combination of physical traits, its hereditary control can hardly proceed beyond the generalized rule that "like
produces like" until the practical stockman is given a more
9specific education on those physical and functional t r a i t s which
act independently in a h e r e d i t a r y sense where close correlation
in h e r e d i t a r y behavior does not exist.
F r o m this point of view the linking up of the men who are
doing this fundamental pioneering in genetics with those of us
who are daily called upon for advice that essentially demands
the practical application of fundamental laws is of historic significance. The contact is stimulating to the geneticist and it is
essential to f u r t h e r progress in practical animal breeding.
THE NEXT ANNUAL DINNER
In keeping with a custom established by the Society an
annual dinner and meeting will be held in honor of one of its
members, whose achievements in the field of animal industry
have been noteworthy. The dinner and meeting for 1923 will
be held Sunday, December 2. Only those who have attended
on f o r m e r occasions can look f o r w a r d with a full appreciation of
this coming event.