1. Sex linked chromosomal abnormalities:
Klinefelter syndrome: The patient has 47 chromosome ; 44 xxy. The testis atrophied and does produce sperm.
Turner Syndrome:
Triple X syndrome: Patient with triple x syndrome are infantile. The triple x syndrome results from fertilization of an xx oocyte and an x sperm.

2. Cell cycle
Many cells of the early embryo are in a constant state of dividing or of preparing to divide. The cell cycle includes four main phases :
S Phase : DNA synthesis.
G2 Phase : A gap phase during which the cell increases in size and prepare to divide.
M Phase : Mitotic phase.
G1 Phase : A gap phase of cell growth and replication of the centrioles.