assume that the female is not only heterozygous for the barred character,
but also for sex, with the female sex-factor dominant. The recessive
character in this case is linked to the female sex chromosome, or,
as Bateson described it, the dominant character is repelled by the
sex-factor. We may make a diagram of the kind given by Morgan if we use
a rod of different shape for the female-producing sex-chromosome, and use
the black rod for the dominant character:--

BARRED female x unbarred male
BX uY uX uX
| \/ |
| /\ |
BX uX uY uX
BARRED male unbarred female
Heterozygous Homozygous


BARRED male x unbarred female
BX BX uX uY
| \/ |
| /\ |
BX uX BX uY
BARRED male BARRED female
Heterozygous Heterozygous

Another case is that of tortoise-shell, _i.e._ black and yellow cats. The
tortoise-shell with very rare exceptions is female, the corresponding male
being yellow, without any black colour. Doncaster found that a yellow male
mated to a black female produced black male offspring and tortoise-shell
females. When a black male is mated to a yellow female, the female kittens