Similarities between spermatogenesis and Oogenesis.

1) Both occur in the germ cells in the gonads.

2) Both produce haploid reproductive units , the gametes, for sexual reproduction.

3) Both consist of 3 phases ; multiplication, growth and maturation.

4) Both involve changes in nucleus as cytoplasm of the gamete mother cells.

Spermatozoon. A spermatozoon consist of four parts; head, neck, middle piece and tail.

Head. The head varies in form in different species it is flat and oval in human sperm. It is composed of large nucleus and a small acrosome. The nucleus is very compact. It consists only of condensed DNA and basic proteins. It lacks RNA, acidic proteins and nucleus.

Acrosome lies at the tip of nucleus. it is formed from the Golgi complex. It contains hydrolytic enzymes, and is used to contact and penetrate. The egg in fertilization. The head is covered by fertilization.

Neck. the neck is very short and contains two centrioles lying one behind and at right angles to the other. The proximal centriole plays a rove in the first cleavage of the zygote. A distal centriole gives rise to the axial filament of the sperm . a centriole itself consists of 9 sets of microtubule triplets arranged in a ring.

Middle Piece. The middle piece varies in shape in different species . It is cylindrical in the human sperm it contains many mitochondria and ATP molecules in a thin layer of cytoplasm. The mitochondria are tightly coiled round the axial filament. They have oxidative enzymes and provide energy for the movement of the sperm in the females genital tract. The amount of energy available is limited. if a sperm fails to contact an ovum within a specific period; it energyand dies.

Tail. The tail is very long, slender and tapering, and is formed of cytoplasm. A fine thread, the axial filament, arises from the posterior centriole and traverses the middle piece and the tail. It may project freely behind the tail as an end piece . The axial filament of the sperm, like that of a flagellum, consists of two single central microtubules surrounded by a ring of mine double microtubules.

Ovum. The ovum is a rounded, non-motile cell. Its size varies in different animals depending upon the amount of yolk in it. However, it is always much large than the other types of cells in the body. I eutherian mammals, including humans, the ovum is almost free of yolk and is said to be alecithal. It has aboundant cytoplasm called ooplasm hang a large nucleus termed germinal vesicle at the centre and surrounded by plasma membrane. The latter gives of microvilli to absorb food materials from the follicular cells during growth. The ovum shows polarity. Its side which extrudes polar bodies is called animal pole. The ovum is enclosed by two additional egg coats; inner thin, transparent, noncellular zona pellucida and outer thick corona radiate formed of radially elongated follicular cells. A narrow perivitelline space exists between the zone pellucida and plasma membrane.