=A Generalized Presence-Absence Formula for Man.--=In man as in lower forms some characters or traits are due presumably to the presence of determiners or to their absence. Likewise, dominance and recessiveness are as much in evidence, for in tracing back pedigrees of various traits we find the same forms of tabulation that obtain for these conditions in plants and lower animals hold good. For typical cases in man let us use a generalized presence-absence formula and the arbitrary symbol A for the presence of the determiner of the character (double in the individual, single in the germ) and a for its absence. Thus AA represents a condition in which similar determiners have been derived from both parents and the individual is _duplex_ as regards the character in question; each mature germ-cell will have the determiner. Aa represents a condition in which the individual has received the determiner from only one parent and is therefore _simplex_ with regard to the character; half of the gametes of such an individual will have the determiner and half will lack it. Lastly, aa represents total absence of the determiner. Such an individual is _nulliplex_. He or she will not have the determiner represented in any of the gametes, and can not, of course, transmit a trait represented by the determiner. It is evident that six kinds of gametic matings are possible among individuals representing these various formulæ. These matings are as follows: Possible couplings Matings of gametes Product 1. Nulliplex x Nulliplex (aa x aa) == a------a == all nulliplex \/ /\ a------a 2. Nulliplex x Simplex (aa x Aa) == a------A == 50 per cent. \/ with character /\ nulliplex and a------a 50 per cent. with it simplex. 3. Nulliplex x Duplex (aa x AA) == a------A == all with characters \/ simplex /\ a------A 4. Simplex x Simplex (Aa x Aa) == A------A == 25 per cent. \/ with characters /\ duplex, 50 per a------a cent. with it simplex and 25 per cent. with it nulliplex.