Cleavage

Definition

Cleavage refers to the early series of mitotic divisions that a fertilized egg undergoes to form a multicellular embryo. This process is crucial in animal development as it leads to the formation of different cell types and ultimately establishes the body plan of the organism. Cleavage patterns can vary among different species, influencing embryonic development and the eventual structure of the adult organism.

5 Must Know Facts For Your Next Test

1. Cleavage results in rapid cell division without significant growth, creating smaller cells called blastomeres.
2. Different species exhibit various cleavage patterns, including radial, spiral, and bilateral cleavage, each affecting how embryos develop.
3. In most animals, cleavage occurs in two distinct forms: holoblastic cleavage, where the entire egg divides, and meroblastic cleavage, where only part of the egg divides.
4. The orientation and timing of cleavage divisions are critical for determining the fate of embryonic cells and their future roles in the organism.
5. Cleavage eventually leads to the formation of structures such as the blastula and sets the stage for subsequent processes like gastrulation and organogenesis.

Review Questions

• How does the pattern of cleavage influence later stages of embryonic development in animals?
  • The pattern of cleavage significantly influences later stages of embryonic development by determining how cells will divide, differentiate, and organize themselves. For example, radial cleavage leads to a symmetrical arrangement that is typical in deuterostomes like humans, while spiral cleavage results in a more complex arrangement found in protostomes. This initial organization affects the embryo's overall body plan and influences developmental pathways during stages like gastrulation.
• Compare and contrast holoblastic and meroblastic cleavage regarding their implications for embryonic development.
  • Holoblastic cleavage involves complete division of the egg into smaller cells, which allows for uniform development in organisms with relatively small yolk content. In contrast, meroblastic cleavage occurs when only a portion of the egg divides due to large amounts of yolk, resulting in an uneven distribution of cells. This difference has important implications for how embryos develop; holoblastic embryos generally form a blastula efficiently, while meroblastic embryos require specialized structures to support growth from the yolk.
• Evaluate how different types of cleavage might affect evolutionary adaptations in various animal lineages.
  • Different types of cleavage can significantly impact evolutionary adaptations by influencing the efficiency and complexity of embryonic development across animal lineages. For instance, organisms with radial cleavage tend to develop more symmetrical body plans which may enhance adaptability to various environmental conditions. In contrast, species exhibiting spiral cleavage may have developed specialized structures or functions that arise from their unique cell arrangements. As a result, these variations in early developmental processes can lead to divergent evolutionary paths that optimize survival and reproduction in differing ecological niches.

Related terms

Blastula: A hollow sphere of cells that forms during early embryonic development following cleavage, leading to further differentiation and development.

Morula: An early stage of embryonic development consisting of a solid ball of cells resulting from cleavage before the formation of the blastula.

Gastrulation:

The phase in embryonic development that follows cleavage, where cells undergo rearrangement to form distinct layers that will develop into various tissues and organs.