T. Lewis and D. Embleton 
53 
animal kingdom, and the term " hybrid " is now given wider scope. Bateson in 
a recent communication lias suggested the applicability of Mendelian laws to 
hereditary pathological and teratological conditions. In the ensuing paragraphs 
the applicability of these laws to hereditary split-foot will be examined ; for if the 
cross between a deformed individual and a normal one is to be designated as a 
hybrid, and if the transmission of any deformity can be shown to proceed along 
Mendelian lines, the question of permanent stability of that deformity upon 
transmission may be considered as settled in the affirmative, and the possibility of 
a human sport originating a species, in the wide sense of the term, will be past 
denial. 
According to the Mendelian doctrine animals and plants cannot be considered, 
from the point of view of heredity, as " units," but as composites of separate 
characters. If as a result of the crossing of two individuals, bearing separate types 
of a single character, these types segregate independently in the offspring, they 
are termed " allelomorphs " and may be expected to obey certain fixed laws. A 
fundamental proposition of Mendelism states that it is impossible for the same 
gamete to carry more than one member of the same pair of allelomorphs. Again, 
one allelomorphic character may show dominance to the other member of the pair, 
in which case the result of the cross between a " dominant " and " recessive " 
allelomorph will be the appearance of offspring all bearing the dominant character*. 
The offspring will nevertheless produce an equal number of gametes carrying 
dominant and recessive characters. Such offspring are termed " heterozygotes," as 
opposed to those arising from the union of like allelomorphic gametes, which are 
termed " homozygotes." When a heterozygote is produced by the union of a 
dominant and a recessive allelomorph, and is crossed with a homozygote resulting 
from the union of two recessive allelomorphs, homozygous offspring bearing the 
recessive character and heterozygotes bearing the dominant character will be 
produced in equal numbers. This principle is illustrated in the accompanying 
diagram (Fig. 3). 
From this necessarily short accountf it may be gathered that when dealing 
with allelomorphic characters an abnormal offspring cannot arise from recessive 
homozygotes, and that in a family tree arising from an abnormal ancestor the 
deformity may be expected to be stable. It also follows that the abnomnal 
offspring of one normal and one abnormal parent is a heterozygote. 
We have seen that there is reason to believe that a sport in all probability 
arises as the result of the union of a normal and an abnormal gamete. It may be 
therefore assumed, if Mendelism is to apply, that the original sport is a heterozygote, 
an assumption which Bateson appears to have made. From this it follows that if 
a family is in agreement with Mendelian laws the total number of deformed and 
undeformed offspring from deformed parents should be equal. 
* If the sport character is recessive, it can never appear in the family unless there is intermarriage, 
t Which for simplicity takes no account of "latency." 
