Morgan, Thomas Hunt, Experimental zoölogy

(New York : London :  The Macmillan Company ; Macmillan & Co., Ltd.,  1907.)

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CHAPTER X

OTHER  KINDS  OF HYBRIDIZING
Blended Inheritance

We have seen in the cases that come under Mendel's law that
the contrasted characters do not both develop at the same time, the
offspring in the first generation being often like one or the other
parent. Yet in some of these cases there is evidence that the
dominant character may be weakened by the recessive one. We
may now consider cases in which the contrasted characters of
the two parents fuse or blend completely in the offspring. Cases
of the sort are found not only between races, varieties, and elemen¬
tary species, but this method of union has long been supposed to
be a characteristic feature of hybridization when Linnsean species
are crossed.

The most familiar and striking case of fusion or blending of
two characters is found in the mulatto — the result of union of a
white and a black individual. The mulatto breeds true in all
successive generations, neither the white nor the negro ever
appearing again in the pure form. If the mulatto again crosses
with the white stock, the dark color is again lessened, but even
after several generations of crossing with the white stock traces
of the dark pigment remain. Conversely crosses between the
mulatto and the black race produce ever increasing shades
of darkness in successive generations of offspring. Not only
the color, but the character of the hair also shows a tendency
to blend in the hybrid.

Flourens made crosses between the domestic dog and jackal,
the latter being, however, "prepotent." The horse and the ass
give the mule,, that is intermediate in many respects, but the

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