Sperm determines sex
SPERM PRODUCTION 1 The primary sperm cell or spermatocyte
includes both an X and a Y chromosome: the two male sex chromosomes.
2 The spermatocyte divides into two secondary spermatocytes,
which each include either an X or a Y chromosome.
3 The two spermatocytes each divide into twospermatids,
two including an X chromosome and two including a Y chromosome.
EGG PRODUCTION 1 The primary egg, the oocyte,
always has two X chromosomes, which would make a girl.
2 During the division,
a secondary egg with an X chromosome and a so-called polar body forms.
3 Prior to the fertilisation, the egg and the polar body divide again,
leaving three useless polar bodies and one egg.
FERTILIZATION 4 The spermatids develop
into sperm cells including tails, which enable them to move towards the egg during fertilisation.
5 Fertilisation is the fusing of a sperm and an ovum.
The egg always has an X chromosome, but a sperm can carry an X (baby is a girl) or a Y (baby is a boy).