PEDIGREE INHERITANCE. 
411 
to be homozygots are not constant, they do not breed true, they are not 
of equal value with the respective pure breeds. The following simple 
experiment goes to show this: 
Pure white breed and pure black breed are descended from the pure 
grey breed. White, grey and black are values of equal measures. The cross 
between white and black is shown in the following pedigree : 
grey grey 
ï ï 
white X black 
The first hybrid generation will be uniform grey. The second gene¬ 
ration is characterized by the white : grey : black = 1:2:1 ratio ; according 
to the Mendelian hypothesis, the greys ought to be hétérozygotie, and the 
whites and the blacks homo zygotic. Let us cross-back a hybrid black 
(recessive, homozygotic) female of the second generation to her pure-bred 
white grandsire. The pedigree of this back-crossing is as follows: 
grey grey grey grey grey grey grey grey 
ïïïïïïïï 
white white white white white black white black 
( white) (whit e) ( grey) (grey ) 
(pure-bred white <J) X (hybrid black $of the 2nd generation) 
(The values enclosed above, between brackets, which answer to two 
generations only, are almost nil, compared with the values which represent 
the full series of ancestry, for which reason they can be omitted from the 
following calculation.) 
If the Mendelian «homozygots» were to be of equal value with the 
pure-bred specimens, they would breed like the latter, and consequently, 
the above mating would also result in a white : grey : black = 1:2:1 Men¬ 
delian ratio, but in reality the ratio which can be deduced from 
the pedigree, viz., 6 : 8: 2 = 3: 4: 1 will be proved in fact. There 
are no homozygots between the half-bred hybrids, which breed true, like, 
and are of equal value with, the pure-bred ancestors. 
The homozygots which breed true inter se , but which are still not 
of equal value with the pure breeds, can be regarded also as the mutations 
of De Vries. Single chances of probability, reversions, variations, extremes 
without intermediates, discontinuous series ; like begets like. 
A new interpretation of Dominance (Uniformity). —White pure breed and 
black pure breed are descended from the grey pure breed. — The pedigree 
ratio of the cross grey x white is consequently 3: 1 on the average. Each 
