Gamete Development
Gamete Development
Gametes are the reproductive cells of an organism. In sexually reproducing organisms, a gamete is a haploid cell that combines with another haploid cell during fertilization. These cells have the ability to become sperm or ova.
Experiment for Stages of Gamete Development
Aim: The aim is to investigate the different stages of Gamete Development in the mammalian testis and ovary.
Tools Required for both TS of Mammalian Testis and Ovaries are Mentioned Below:
Compound microscope.
Permanent slides of T.S of mammalian ovary and testis.
Lens clearing papers.
Cleaning fluid.
Let’s proceed with the process of conducting TS of mammalian ovary and testis.
Principle
Gamete creation takes place in the gonads of all male and female organisms, which are the testis and ovary, respectively.
Meiotic cell division is required for gamete creation, which is referred to as gametogenesis.
Spermatogenesis is the gametogenic development in the testis, while oogenesis is the gametogenic development in the ovary. They have distinct characteristics that can be seen in the transverse sections (T.S.) of these organs.
Procedure
First, wash hands properly and dry them thoroughly.
With the help of lens cleaning paper and cleaning fluid, clean the slide, microscope’s eye, and objective lens.
Place the slide on the microscope stage.
Start observing under lower magnification and then proceed towards higher magnification.
Write down your observations in a biology practical copy. Now draw diagrams of both TS of mammalian ovary and testis and label them.
Transverse Section of Testis
The testis is the most vital male reproduction organ. It is responsible for producing male gametes or sperms and storing them. Also, it forms testosterone hormones that influence sex drive, fertility and increases bone mass and muscle power.
Male humans have a pair of the testis. The process of gametogenic development in testes is known as spermatogenesis.
TS of testis under microscope shows these components.
Observation
Lower magnification will reveal a huge number of seminiferous tubules. They are somewhat round or oval.
View several stages of gamete growth from the periphery to the lumen and a full tubule under increased magnification.
Evaluate the following types of cells:
Germinal epithelium
Spermatogonial cells
Primary spermatocytes
Secondary spermatocytes
Spermatids
Spermatozoa
The space between tubules in T.S. of the testis is filled with blood vessels and a special cell type known as Leydig's cell or Interstitial cells.
Also, you can see Sertoli cells that hold the sperms.
However, the mature sperms remain inside the lumen of the Seminiferous tubule. In this stage, the sperm has ahead and tell, but the middle is still immature.
Fill in the gap: Sertoli cells are separated by _______________ cells.
Ans: Spermatogenic.
Now, draw the TS of the mammalian testis diagram and label it.
Transverse Section of Ovary
Ovaries are the primary reproductive organs of almost all female vertebrates. Their main function of them is to produce female gametes or eggs. Also, they are responsible for forming progesterone hormones.
Most mammals, including female humans, possess two ovaries, right and left.
The development of gametes inside ovaries is called oogenesis.
TS of mammalian ovaries will help you to study the several components of ovaries.
Observation
There is a mass of tissue lined with germinal epithelium in the ovarian region.
You'll find an ovum inside, which is a single cell surrounded by one to several layers of follicular cells. Furthermore, one or several layers of follicular cell guard the ovum. The number of follicular cell layers increases as the ovum matures.
The number of surrounding follicular cell layers grows as the ovum matures.
Later in follicular development, an antrum cavity occurs.
The cavity and the follicle enlarges. The Graafian follicle has reached the stage where it is ready to discharge the ovum. This process is called ovulation.
A Corpus luteum and/or Corpus Albicans, which differ in appearance from one another and from the Graafian follicle which can be seen at the next stage.
They also differ from the follicular cell. Corpus Luteum forms from the ruptured follicle that contains Lutein cells and is surrounded by blood clots.
Atretic follicle shows that the follicle cells are disorganised. It also carries the sign of nuclear necrosis. Moreover, it also shows the reduced size of the oocyte.
All these stages are clearly seen in the permanent ovary slide.
FAQs on Stages of Gamete Development
1. What is gametogenesis, and what are its two primary types in humans?
Gametogenesis is the biological process by which diploid precursor cells undergo meiotic division to form haploid gametes (sex cells). In humans, this process is essential for sexual reproduction. The two primary types are:
- Spermatogenesis: The formation of sperm (spermatozoa) in the male testes.
- Oogenesis: The formation of the egg (ovum) in the female ovaries.
2. What are the key stages of spermatogenesis in human males?
Spermatogenesis is a continuous process that begins at puberty and occurs in the seminiferous tubules of the testes. The stages are:
- Spermatocytogenesis: Diploid spermatogonia (stem cells) multiply by mitosis and then grow to become primary spermatocytes.
- Meiosis I: Each diploid primary spermatocyte divides to form two haploid secondary spermatocytes.
- Meiosis II: The two secondary spermatocytes divide to form four haploid spermatids.
- Spermiogenesis: The non-motile spermatids undergo a transformation to become mature, motile spermatozoa (sperm).
3. What are the stages of oogenesis, and how does it differ from spermatogenesis?
Oogenesis is the process of forming a mature ovum and begins before birth. The stages are:
- It starts with a diploid oogonium in the foetal ovary, which grows into a primary oocyte and enters Meiosis I, but gets arrested in Prophase I.
- At puberty, one primary oocyte resumes division to form a large haploid secondary oocyte and a tiny first polar body.
- The secondary oocyte begins Meiosis II but gets arrested in Metaphase II.
- This arrest is only broken if fertilisation occurs, completing Meiosis II to form the mature ovum and a second polar body.
4. What is the fundamental difference between a germ cell and a mature gamete?
The fundamental difference lies in their chromosome number and developmental stage. A germ cell (like a spermatogonium or oogonium) is a diploid (2n) precursor cell found in the gonads. It is the starting point of gametogenesis. A mature gamete (sperm or ovum) is the final product, which is haploid (n) and has undergone both meiotic divisions and differentiation to become capable of fertilization.
5. Why are human gametes (sperm and ovum) considered haploid?
Human gametes are considered haploid because they contain only one set of chromosomes (n=23). This is a result of the meiotic cell division they undergo during gametogenesis, which reduces the chromosome number by half. This haploid state is crucial for sexual reproduction, as the fusion of a haploid sperm and a haploid egg during fertilization restores the normal diploid (2n=46) chromosome number in the resulting zygote.
6. How do hormones like GnRH, LH, and FSH regulate the stages of gamete development?
Hormones create a precise control system. The hypothalamus releases Gonadotropin-releasing hormone (GnRH), which stimulates the anterior pituitary to secrete two key hormones:
- Luteinizing Hormone (LH): In males, LH stimulates the Leydig cells to produce testosterone, which is essential for spermatogenesis. In females, an LH surge triggers ovulation and supports the corpus luteum.
- Follicle-Stimulating Hormone (FSH): In males, FSH acts on Sertoli cells to nourish developing sperm cells. In females, FSH stimulates the growth and maturation of ovarian follicles, which contain the developing oocyte.
7. Why does oogenesis result in one large ovum and smaller polar bodies, while spermatogenesis produces four equal spermatids?
This difference is due to the biological function of each gamete. Oogenesis involves unequal cytokinesis (cytoplasm division) because its goal is to produce one large, highly resourceful cell. The ovum retains almost all the cytoplasm, nutrients, and organelles to support the embryo after fertilization. The polar bodies are essentially non-functional cells that just serve to discard the extra sets of chromosomes. In contrast, the goal of spermatogenesis is to produce millions of small, motile gametes, so equal division is more efficient for maximizing sperm count.
8. At which specific stages is oogenesis arrested, and what is the biological importance of this pause?
Oogenesis is arrested at two key stages:
- First Arrest: In Prophase I of meiosis. This occurs in all primary oocytes within the foetal ovary and lasts until puberty.
- Second Arrest: In Metaphase II of meiosis. This occurs after ovulation, and the secondary oocyte will only complete this stage if it is fertilized by a sperm.
9. How can you identify the different stages of spermatogenesis in a T.S. of a mammalian testis?
In a transverse section (T.S.) of a mammalian testis, you can observe the stages within the seminiferous tubules. The cells are arranged in an orderly sequence from the outer edge to the inner lumen:
- Spermatogonia: Small, diploid cells found along the periphery (basement membrane).
- Primary Spermatocytes: Larger cells, also diploid, located just inward from the spermatogonia.
- Secondary Spermatocytes: Smaller, haploid cells that are less commonly seen as they quickly divide.
- Spermatids: Small, round, haploid cells found closer to the lumen.
- Spermatozoa: Mature sperm with visible heads and tails, often with their tails extending into the lumen of the tubule.
10. What is the importance and function of the corpus luteum in the female reproductive cycle?
The corpus luteum is a temporary endocrine gland that forms from the remnants of the ovarian follicle after ovulation. Its primary function is to secrete high levels of progesterone, and some estrogen. Progesterone is vital for preparing the uterus for pregnancy by thickening the endometrium (uterine lining), making it receptive to implantation. If fertilization does not occur, the corpus luteum degenerates, causing progesterone levels to drop and triggering menstruation.
