20 FARM ANIMALS 
be all the same as far as the eye can tell) one-third of them (pure 
dominants) when inbred, will yield the normal mice, the other two- 
thirds (impure dominants) will split up again, when inbred, into 
normal mice and waltzing mice in the old proportion of 3:1.” 
13. Pure-bred races.—Often there is found certain 
characteristics that distinguish a family or variety from 
one or others of that race. These distinctions give rise 
to breeds, into which all of our 
domestic animals have been 
grouped. Thus the Yorkshire 
hog differs from a hog of the 
Poland-China in color, confor- 
mation, bone and in other traits. 
These differences of breed are 
possibly due to climate, food, 
habit and environment. When 
a breed has been under the same © 
environment for considerable 
time and has not been crossed 
with hogs of a different environ- 
ment or breed, the race becomes 
established, and individuals are 
OF THE SAME ANCESTRY 
Yorkshire at top, Poland-China Pure bred. Ifa record is kept of 
at bottom. Their ancestry traces 4. s 
back to the wild boar of the woods, the ancestry, it is known as its 
pedigree. Pedigrees are re- 
corded by breed associations, the book of such records 
being called a herd book. 
14. Scrub stock.—Farm animals of no known breeding 
or of mongrel and degenerated qualities are called scrub 
stock. As a rule these are unsatisfactory because such 
individuals are not profitable as are those of selected 
strains. Scrub stock is fast being replaced by individuals 
of pure breeding or by those “bred-up” through the use 
of pure-bred sires. 
