“special” chromosome is present in the cells of the male individuals which
was called Y-chromosome. Since it proved that these two types of
chromosomes are connected with the determination of sex they were called
sexual chromosomes.
Wilson and Stevens have suggested a comparatively simple mechanism
of distribution of the sexual chromosomes in the process of cell division. They
have assumed that each egg and the half of the spermatozoa have an X-chromosome.
The other half the spermatozoa contains the Y- chromosome.
When the egg is fertilized by a spermatozoon with an X-chromosome a
zygote of two X-chromosomes (XX) is obtained which gives rise to an
individual of the female sex. When the fertilization is carried out by a
spermatozoon with a Y-chromosome then the zygote has the two types (XY)
and an individual of the male sex is developed from it (Fig. 2–14).
image
Figure 2–14. Scheme for determining of the sex depending on the presence and combination of the X- and Y-chromosomes in the migratory short-tentacled locust (Dichroplus silveira guidoi) with four chromosome pairs (2n=8). (After De Robertis et al., 1973).