ltogether, as is
now so often the case.

The application of Mendelian principles is likely to prove of more
immediate service for plants than animals, for owing to the large numbers
which can be rapidly raised from a single individual and the prevalence of
self-fertilisation, the process of analysis is greatly simplified. Even
apart from the circumstance that the two sexes may sometimes differ in
their powers of transmission, the mere fact of their separation renders the
analysis of their properties more difficult. And as the constitution of the
individual is determined by the nature and quality of its offspring, it is
not easy to obtain this knowledge where the offspring, as in most animals,
are relatively few. Still, as has been abundantly shown, the same
principles hold good here also, and there is no reason why the process of
analysis, though more troublesome, should not be effectively carried out.
At the same time, it affords the breeder a rational basis for some familiar
but puzzling phenomena. The fact, for instance, that certain characters
often "skip a generation" is simply the effect of dominance in F_1 and the
reappearance of the recessive character in the following generation.
"Reversion" and "atavism," again, are phenomena which are no longer
mysterious, but can be simply expressed in Mendelian terms as we have
already suggested in Chap. VI. The occasional appearance of a sport in a
supposedly pure strain is {166} often due to the reappearance of a
recessive character. Thus even in the most highly pedigreed strains of
polled cattle such as the Aberdeen Angus, occasional individuals with horns
appear. The polled character is dominant to the horned, and the occasional
reappearance of the horned animal is due to the fact that some of the
polled herd are heterozygous in this character. When two such individuals
are mated, the chances are 1 in 4 that the offspring will be horned. Though
the heterozygous individuals may be indistinguishable in appearance from
the pure dominant, they can be readily separated by the breeding test. For
when crossed by the recessive, in this case horned animals, the pure
dominant gives only polled beasts, while the heterozygous individual gives
equal numbers of polled and horned ones. In this particular instance it
would probably be impracticable to test all the cows by crossing with a
horned bull. For in each case it would be necessary to have several polled
calves from each before t