(1) M and mimetics in about equal numbers.
(2) M and mimetics in the ratio of about 1:3.
(3) Mimetics only.
The males are in all cases alike to look at but it must nevertheless be supposed that they differ in their transmitting powers. In fact the evidence all points to there being three different kinds of male corresponding to the three different kinds of female. But they cannot shew any difference outwardly because there is always present in the male a factor which inhibits the production of the mimetic pattern even though the factor for that pattern be present.
Returning now to the records of the females it will be noticed that although the M form may breed true the mimetics never give the M form alone. Where they give the M form among their progeny they produce mimetics and non-mimetics either in the ratio 1:1 or of 3:1. This at once suggests that the
non-mimetic is recessive to the mimetic forms—that the mimetics contain a factor which does not occur in the non-mimetics. If this factor, which may be called X, be added to the constitution of a non-mimetic female it turns it into a mimetic. If X be added to a male such an individual, though incapable of itself exhibiting the mimetic pattern owing to the inhibitory factor always present in that sex, becomes capable of transmitting the mimetic factor to its offspring. Expressed in the usual Mendelian way the formulae for these different butterflies are as follows:—
| M♀ | = | or iixx | Iixx | = ♂ (1) |
| Mimetic |  =  | or iiXX | IiXX | = ♂ (2) |
| ♀♀ | or iiXx | IiXx | = ♂ (3) |
where X stands for the mimetic factor and I for the factor which inhibits the action of X. All males are heterozygous for I, but during the segregation of characters at some stage in the formation of the families only the male-producing sperms come to contain the factor I. It is lacking in all the female-producing sperms formed by the male.
♂ (1) does not contain the factor for the mimetic condition and gives only daughters of the M form when mated with an M♀. ♂ (2) on the other hand is homozygous for the factor X, and consequently all of his germ cells contain it. This is the male that gives nothing but mimetic daughters with whatever form of female he is bred. ♂ (3) is heterozygous for X; that is to say, one half of his germ cells contain it, the other half not. With the M♀ he must give equal numbers
of offspring with and without X, i.e. half of his daughters will be mimetic and the other half non-mimetic. With a heterozygous mimetic female (iiXx), which is also producing germ cells with and without X in equal numbers, he may be expected to give the usual result, viz. dominants and recessives in the ratio 3:1; or in other words mimetic and non-mimetic females in the ratio 3:1.