But there are additional and even more significant deductions from the facts. We have seen that the gametes are differentiated in respect of pure characters. Of these pure characters there may conceivably be any number associated together in one organism. In the pea Mendel detected at least seven—not all seen by him combined in the same plant, but there is every likelihood that they are all capable of being thus combined.
Each such character, which is capable of being dissociated or replaced by its contrary, must henceforth be conceived of as a distinct unit-character; and as we know that the several unit-characters are of such a nature that any one of them is capable of independently displacing or being displaced by one or more alternative characters taken singly, we may recognize this fact by naming such unit-characters allelomorphs. So far, we know very little of any allelomorphs existing otherwise than as pairs of contraries, but this is probably merely due to experimental limitations and the rudimentary state of our knowledge.
In one case (combs of fowls) we know three characters, pea comb, rose comb and single comb; of which pea and single, or rose and single, behave towards each other as a pair of allelomorphs, but of the behaviour of pea and rose towards each other we know as yet nothing.
We have no reason as yet for affirming that any phenomenon properly described as displacement of one allelomorph by another occurs, though the metaphor may be a useful one. In all cases where dominance has been perceived, we can affirm that the members of the allelomorphic pair stand to each other in a relation the nature
It is not the ancestral type that has come back, but something else has come in its guise, as the offspring presently prove. For the first time we thus begin to get a rationale of "reversion."
