I. Proliferative zone
The initial stage of gametogenesis is characterized by active division of primordial germ cells.
The main type of division in this zone is mitosis. Due to mitotic divisions, the cellular pool accumulates without loss of genetic information. The genetic set of cells at this stage is $2n2c$ (diploid set of chromosomes with normal, unduplicated DNA content).
Depending on sex, different cells are formed:
- During spermatogenesis, spermatogonia are formed.
- During oogenesis, oogonia are formed.
II. Growth zone
Cells cease mitotic division and enter the phase of active preparation for reductional division. In terms of the cell cycle, this zone corresponds to interphase.
The main event of the growth zone is DNA replication (doubling). As a result, the genetic formula changes to $2n4c$: the chromosome set remains diploid, but the amount of DNA is doubled.
Cells increase significantly in size and receive new names:
- In the male body, these are primary spermatocytes.
- In the female body, primary oocytes.
III. Maturation zone
This zone undergoes meiosis (reductional division), which consists of two consecutive stages.
1. Meiosis I The first division leads to the formation of cells with a haploid set and doubled chromatids ($n2c$).
- Spermatogenesis: one primary spermatocyte forms 2 equivalent cells — secondary spermatocytes.
- Oogenesis: division occurs asymmetrically. 1 large cell (secondary oocyte) and 1 small polar body are formed.
2. Meiosis II The second division completes the reduction process. The genetic set takes its final form — $nc$ (haploid set, single chromatid).
- Spermatogenesis: 4 identical cells are formed — spermatids.
- Oogenesis: 1 large ovum and 3 small polar bodies are formed.
IV. Differentiation zone
The final phase, which exhibits pronounced sexual dimorphism.
It is present only in spermatogenesis. In oogenesis, this stage is absent (or not distinguished in the classical scheme).
At this stage, the genetic set remains unchanged ($nc$). Complex morphological reorganization occurs: spermatids transform into mature spermatozoa. The main visual difference is the appearance of a specific locomotive apparatus — the flagellum (tail).
Comparison table
| Characteristic | Proliferative zone | Growth zone | Maturation zone | Differentiation zone |
|---|---|---|---|---|
| Type of division | Mitosis | Interphase | Meiosis | Transformation |
| Set | $2n2c$ | $2n4c$ | $n2c \rightarrow nc$ | $nc$ |
| Spermatogenesis | Spermatogonia | Primary spermatocytes | Secondary spermatocytes $\rightarrow$ Spermatids | Spermatozoa |
| Oogenesis | Oogonia | Primary oocytes | Secondary oocyte $\rightarrow$ Ovum | Absent |
Briefly: answers to topical questions
What do the morphological transformations of spermatids consist of in the differentiation zone?
In the differentiation zone, spermatids transform into spermatozoa through a series of structural changes.
The process includes the following morphological reorganizations:
- Chromatin in the nucleus condenses.
- A flagellum forms from the centrioles (tail formation).
- The acrosome forms from the Golgi apparatus.
- Mitochondria cluster at the base of the tail to form a sheath.
- Cytoplasmic bridges connecting the clone of cells disappear.
- Excess cytoplasm is phagocytosed by cells.
During which period of ontogenesis does the proliferative zone occur in oogenesis and spermatogenesis?
The periods of passing through the proliferative zone vary significantly depending on the type of gametogenesis.
| Process | Period of proliferation zone progression |
|---|---|
| Oogenesis | Occurs intrauterinely, from the 3rd to the 6th–7th month of embryogenesis |
| Spermatogenesis | Begins at puberty and continues almost until death |
To memorize the order of the zones, use the mnemonic PRSF: Proliferation, Growth, Maturation, Spermiogenesis (Formation).
Class and exam questions
In which zone does DNA replication occur?
DNA replication occurs in the growth zone, which corresponds to the interphase of the cell cycle. The genetic complement changes from $2n2c$ to $2n4c$.
Why are polar bodies formed in oogenesis?
During meiosis in the maturation zone, the cytoplasm divides unequally to provide the future oocyte with a maximum supply of nutrients. The smaller cells are called polar bodies.
What is the genetic complement of a secondary spermatocyte?
The secondary spermatocyte is formed after the first meiotic division and has a haploid set with doubled chromatids — $n2c$.
What else to study on this topic
- Features of mitosis during the formation of spermatogonia and oogonia
- Mechanisms of DNA replication in interphase (growth zone)
- Differences between meiosis I and meiosis II in the maturation zone
- Biological significance of polar body formation in oogenesis
- Morphological changes of spermatids in the formation zone
Master the entire topic in the "Biology" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Zones of Gametogenesis" and 3,793 more pages for this subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 129 video lessons on the subject
Other topics in the "Gametogenesis" section
Free video lessons: BiologyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.