The main difference between gametogenesis and embryogenesis is that both meiosis and mitosis occur during gametogenesis whereas only mitosis occurs during embryogenesis. Furthermore, gametogenesis is responsible for the production of male and female gametes while embryogenesis is responsible for the formation and the development of the embryo.
Gametogenesis and embryogenesis are two consequential processes related to the sexual reproduction of organisms. Therefore, both processes are responsible for the production of an offspring.
Key Areas Covered
1. What is Gametogenesis
– Definition, Process, Importance
2. What is Embryogenesis
– Definition, Process, Importance
3. What are the Similarities Between Gametogenesis and Embryogenesis
– Outline of Common Features
4. What is the Difference Between Gametogenesis and Embryogenesis
– Comparison of Key Differences
Key Terms
Cleavage, Embryo, Embryogenesis, Gametes, Gametogenesis, Gastrulation, Meiosis, Mitosis, Neurulation, Oogenesis, Organogenesis, Spermatogenesis, Zygote
What is Gametogenesis
Gametogenesis is the process responsible for the formation of haploid sex cells or gametes, starting either from diploid or haploid precursor cells. The two main phases of gametogenesis are cell division and maturation. In animals, it occurs in gonads, while in plants, it occurs in gametangia. Also, based on the type of sex cells produced, there are two types of gametogenesis as oogenesis and spermatogenesis. Furthermore, oogenesis is the formation of female gametes, which occurs in the ovaries and archegonia, respectively. On the other hand, spermatogenesis is the formation of male gametes, which respectively occurs in testis and antheridia.
Figure 1: Gametogenesis
Furthermore, both oogenesis and spermatogenesis proceed through four common steps:
- Gametocytogenesis – mitosis of the diploid precursor cells of the gametogonium
- Gametidogenesis I – meiosis I of the primary gametocytes
- Gametidogenesis II – meiosis II of the secondary gametocytes
- Maturation – the maturation of the secondary gametocyte into either a male or female gamete
What is Embryogenesis
Embryogenesis is the formation and the development of a multicellular embryo from the unicellular zygote. It starts with the fertilization of a male and a female gamete, forming the zygote, a diploid cell. In humans, the embryonic stage lasts for about 58 days from 5 to 11 weeks. The later phase of development is known as fetal development. Especially, the four steps of the embryogenesis include cleavage, gastrulation, neurulation, and organogenesis.
Cleavage
Cleavage is the cell division without significant growth. Here, the formed cell cluster has the same size as the zygote. Also, based on the amount of yolk in the fertilized egg, holoblastic and meroblastic cleavage are the two types of cleavage. In holoblastic cleavage, total cleavage occurs while in meroblastic cleavage, only a partial cleavage occurs. The stage with 16 cells is known as the morula, which undergoes the blastula stage to become a blastula. Initially, the cell mass produced by the cleavage undergoes blastulation in which an outer layer of cells called the trophoblast, and an inner cell mass are formed. Then, the inner cell mass further differentiates to form an embryoblast polarized at one end. The cavity that forms as a result of this polarization is known as blastocoel. Now, this stage is known as the blastocyst or blastula in mammals.
Figure 2: The First Few Weeks of Embryogenesis in Humans
Furthermore, the embryoblast forms a bilaminar embryonic disk, giving rise to three germ layers. Here, the upper layer of the embryonic disk or the epiblast develops into the ectoderm. Also, hypoblast or the lower layer develops into the endoderm. After that, the formation of a primitive streak starts on the surface of the epiblast, undergoing invagination, which refers to the movement of cells of the epiblast towards the primitive streak and slipping beneath. Also, some cells of the hypoblast migrate into the endoderm, and some migrate in between the endoderm and epiblast to form the mesoderm.
Gastrulation
Gastrulation is the developmental process of the single-layered blastula into a multi-layered gastrula. Significantly, the formation of the primitive streak marks the beginning of the gastrulation. During gastrulation, the primitive streak is responsible for the establishment of the bilateral symmetry. Therefore, gastrulation is responsible for giving a specific head-to-tail and front-to-back orientation to the embryo.
Figure 3: Gastrulation
Neurulation
Neurulation is the transformation of the neural plate into the neural tube. Neurula refers to the stage of embryo undergone neurulation. Neurulation starts with the formation of a primitive node in front of the primitive streak. Here, the primitive node is developed by the epiblast, and it induces the formation of the neural plate. Significantly, the neural plate is the basis of the nervous system, and it folds upon to form the neural tube.
Figure 4: Neurulation
Organogenesis
Organogenesis is the development of organs at the end of the gastrulation. During organogenesis, the three germ layers, ectoderm, endoderm, and mesoderm, develop into the internal organs of the body through cell differentiation and specialization.
Figure 5: Differentiation of the Three Germ Layers
Similarities Between Gametogenesis and Embryogenesis
- Gametogenesis and embryogenesis are two sequential processes of the sexual reproduction of organisms.
- They occur in both animals and plants.
- Also, both are responsible for the production of a new individual through the formation of the zygote.
- Besides, both processes occur through cells division while mitosis is an essential type of cell division in both processes.
Difference Between Gametogenesis and Embryogenesis
Definition
Gametogenesis refers to the development of mature haploid gametes from either haploid or diploid precursor cells while embryogenesis refers to the process by which the embryo forms and develops.
Significance
The main difference between gametogenesis and embryogenesis is that gametogenesis is the formation of male and female gametes while embryogenesis is the formation and the development of an embryo from the zygote.
Occurrence
Gametogenesis occurs in the ovaries and testis in animals and in the archegonia and antheridia in plants. In contrast, embryogenesis occurs inside the female reproductive system in animals while in plants it occurs in the female gametophyte. Thus, this is another difference between gametogenesis and embryogenesis.
Consequence
Furthermore, while gametogenesis occurs prior to fertilization, fertilization is followed by the embryogenesis.
Type of Cell Division
Both meiosis and mitosis occur during gametogenesis while only mitosis occurs during embryogenesis. Hence, this is another major difference between gametogenesis and embryogenesis.
Process
Moreover, gametocytogenesis, gametidogenesis I, gametidogenesis II, and maturation are the four steps of gametogenesis while cleavage, gastrulation, neurulation, and organogenesis are the four steps of embryogenesis.
Importance
Also, the two types of gametogenesis are oogenesis and spermatogenesis while embryogenesis leads to organogenesis.
Ploidy of the Resultant Cells
Another difference between gametogenesis and embryogenesis is that gametogenesis forms haploid gametes while embryogenesis forms diploid cells of the embryo.
Conclusion
Gametogenesis is the formation of gametes from their precursor cells. Here, the formation of male gametes is known as spermatogenesis while the formation of female gametes is known as oogenesis. Primarily, they undergo meiosis, mitosis, and maturation. In comparison, embryogenesis is the formation and the development of the embryo from the unicellular zygote. Moreover, this process only undergoes mitosis. Therefore, the main difference between gametogenesis and embryogenesis is the type of process and the type of cell division.
References:
1. “Gametogenesis|Biology for Majors II.” Lumen Learning, Lumen, Available Here
2. “Human Embryogenesis.” Khan Academy, Khan Academy, Available Here
Image Courtesy:
1. “Gray’s 7 (ovum maturation)” By Fred the Oyster – Own work (Public Domain) via Commons Wikimedia
2. “HumanEmbryogenesis” By Zephyris – SVG version of . (CC BY-SA 3.0) via Commons Wikimedia
3. “Blastula” By Abigail Pyne – Own work (Public Domain) via Commons Wikimedia
4. “Neural crest” By NikNaks – File:Neural_Crest.png (Public Domain) via Commons Wikimedia
5. “Germ layers” By CNX (CC BY-SA 3.0) via Commons Wikimedia
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