e sons have inherited the peculiarity from the mother (fig. 38B). Here
again the result is the same as for the similar combination in Drosophila.

[Illustration: FIG. 61. Spermatogenesis in man. There are 47 chromosomes
(diploid) in the male. After reduction half of the sperm carry 24
chromosomes (one of which is X) and half carry 23 chromosomes (no X).]

In man the sex formula appears to be XX for the female and XO for the male
(fig. 60), and since the relation is essentially the same as that in
Drosophila the chromosome explanation is the same. According to von
Winiwarter there are 48 chromosomes in the female and 47 in the male (fig.
61). After the extrusion of the polar bodies there are 24 chromosomes in
the egg. In the male at one of the two maturation divisions the X
chromosome passes to one pole undivided (fig. 61, C). In consequence there
are two classes of sperms in man; female producing containing 24
chromosomes, and male producing containing 23 chromosomes. If the factor
for color blindness is carried by the X chromosome its inheritance in man
works out on the same chromosome scheme and in the same way as does white
eye color (or any other sex linked character) in the fly, for the O sperm
in man is equivalent to the Y sperm in the fly.

In these cases we have been dealing with a single pair of characters. Let
us now take a case where two pairs of sex linked characters enter the cross
at the same time, and preferably a case where the two recessives enter the
cross from the same parent.

If a female with white eyes and yellow wings is crossed to a wild male with
red eyes and gray wings (fig. 62), the sons are yellow and have white eyes
and the daughters are gray and have red eyes. If two F_1 flies are mated
they will produce the following classes.

[Illustration: FIG. 62. Cross between a white eyed, yellow winged female of
D. ampelophila and a red eyed, gray winged male. Two pairs of sex linked
characters, viz., white-red and yellow-gray are involved. (See text.)]

Yellow Gray Yellow Gray
White Red Red White
------------ -------------
| |
99.% 1.%

Not only have the two grandparental combinations reappeared, but in
addition two new combinations, viz., grey white and yellow red. The two
original combinations far exceed in numbers the new or exchange
combinations. If we follow the history of the X chromosomes we discover
that the _larger classes_ of gr