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 F1 flies are mated they will produce the following classes.
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.)