296 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [VI, III
indicate partial dominance of the longer wool, but if amount of fibre (i.e. volume)
is considered, then these conclusions may have to be modified, since in this cross
the F 2 average fibre-volumes tend to swing towards the Cheviot parental type
rather than the Border Leicester [8].
If we admit that multiple-factor systems determine fleece-character inherit-
ance, two important considerations arise. The first is the apparent futility of
searching for single genetic factors which may override or profoundly affect the
fleece-complex of wool characters. Miller [1] has raised this point, but re-emphasis
is not out of place. The second concerns methods and degrees of selection. The
suggestion can be made that some of the divergent results of investigations are
explicable on the grounds that one parental form has been selected more rigorously,
or is less heterozygous, for one particular fleece-character and exhibits a degree of
prepotency, just as in ordinary breeding practice appear strains or individuals
decidedly impressive. Conceivably, such an interpretation may be applicable,
for example, in the first and second generations of the Border Leicester-Cheviot
cross, which show bimodal frequency distributions of fibre-length similar to those
found in the Border Leicester [8].
Selection for wool-productivity is in practice pursued within the single breed
or flock ; in ordinary husbandry its objects are generally to reduce the variability
of fibre-character on each animal and from one animal to another, i.e. within the
flock or breed, as well as to improve performance in some desired directions, such
as greater density, higher fleece-weight, better yield or longer staple. Outstand-
ing examples of the progress of such selection are to be found among the
' stud ' Merino flocks, and from them we can draw conclusions, not only as to the
methods of improvement, but also as to the ways in which the geneticist may
accompany the practical breeder.
In multiple-factor situations, the phenotype closely reflects the genotype.
In the stud flocks, we find that whereas first selection may be phenotypic, the
progeny test is widely applied, and the method of breeding involves a progressive
infiltration of a genotype throughout part of the flock. Thus, briefly, a stud ram
will be mated to a few selected stud ewes, some of his ram offspring will be mated
to other stud ewes, and so on, until, when proved, his influence can be applied where
necessary in the flock. Even in the larger commercial flocks, some selected ewes
are retained almost solely for use with introduced rams, to breed rams for general
service, forming a ram-testing and breeding flock within the main flock. But the
function of the studs, or pedigree flocks, is to supply so-called ' flock rams' for
use elsewhere, which means, in many different environments. The breeders
realize the importance of the extra-ordinary effects of environment on the animal
and its fleece; hence a certain variability of genotype is deliberately maintained
so that the different demands for flock rams may be met. To this end the
variability is kept possibly relatively greater among the top stud animals than
among the flock ewes.