Thus, if we indicate the dominant character by _D_ and the recessive
by _d_, the constitution of the two individuals is

_Dd_ and _dd_.

The gametes they produce are

_D+d_ and _d+d_,

and the fertilisations are therefore

_Dd_, _Dd_, _dd_, _dd_,

or heterozygote dominants and pure recessives in equal numbers.

It is evident that the reproduction of the sexes is very similar to this.
One of the remarkable facts about sex is that, although the uniting
gametes are male and female yet they give rise to males and females in
equal numbers. If one sex were a dominant this would be in accordance with
Mendelian theory. In accordance with the view that the dominant is
something present which is absent in the recessive, the Mendelian theory
of sex assumes that femaleness is dominant, and that maleness is the
absence of femaleness, the absence of something which makes the individual
female. If we represent the character of femaleness by _F_ and maleness or
the recessive by _f_, we have the ordinary sexual union represented by

_Ff_x_ff_;

the gametes will then be