Topic 5.2. Gametogenesis

Gametogenesis - formation of gametes. Gametes develop in the gonads (sex cells).

In males, it is spermatogenesis, formation of sperm.

In females, it is oogenesis, formation of ova.

Spermatogenesis - Process by which spermatogonia differentiate into mature spermatozoa. Begins at puberty. Spermatozoa are formed in the wall of seminiferous tubules of the testes.

Stages in Spermatogenesis

• Many cells of different sizes and shapes:

(a) Various cell stages in spermatogenesis

(b) Sertoli (sustentacular) cells

• Sertoli cells provide support and nutrition to germ cells.

• Regulated by luteinising hormone (LH). • It binds to Leydig cells to stimulate testosterone production.

Spermiogenesis • The process of transformation of a circular spermatid to a spermatozoon is called spermiogenesis.

• Golgi phase

• Cap phase

• Acrosomal phase

• Maturation phase

Spermatozoon - An actively motile, free swimming cell. Consists of a head, neck and a tail (flagellum). Head: ovoid, consists of nucleus. The anterior 2/3 rd of nucleus is covered by acrosomal cap. Tail has 3 segments: middle piece, principal piece and end piece.

Oogenesis - Occurs in the ovaries and in the oviducts. Starts before birth. Ovary has cortex & medulla. Oogonia are present in cortex. Oogonia are produced at a very early stage (before birth) and do not multiply thereafter.

Oogenesis - After Telophase I and II, the cytoplasm is not equally divided. One of the new cells gets the majority and it survives, while the other one, a polar body, gets broken down.

IMPORTANT TERMS

Gamete: egg or sperm

Gametogenesis: process of formation and development of gametes

Oogenesis: production of eggs

Spermatogenesis: production of sperms

Spermiogenesis: differentiation of sperm morphology

Follicle: where eggs mature in the ovary

Ovulation: release of egg from follicle

Polar body: nonfunctional product of meiotic divisions in oogenesis

Zygote: Fertilized egg