Holoblastic

Definition

Holoblastic describes a type of cleavage in embryonic development where the entire egg is divided into smaller cells. This occurs in eggs with little to moderate yolk content, such as those of mammals and amphibians.

5 Must Know Facts For Your Next Test

1. Holoblastic cleavage results in the complete division of the egg into blastomeres.
2. It occurs in species with isolecithal or mesolecithal eggs, which have uniformly or moderately distributed yolk.
3. Types of holoblastic cleavage include radial, spiral, bilateral, and rotational cleavage.
4. In mammals, holoblastic cleavage leads to the formation of a blastocyst.
5. Amphibians exhibit holoblastic cleavage despite having moderate yolk due to their evolutionary adaptations.

Review Questions

• What type of eggs undergo holoblastic cleavage?
• How does holoblastic cleavage differ from meroblastic cleavage?
• Name at least two types of holoblastic cleavage patterns.

Related terms

Meroblastic: Cleavage where only part of the egg divides, typical in eggs with a large amount of yolk.

Blastomere: A cell formed by the division of a fertilized egg during early embryonic development.

Blastocyst: A structure formed in early mammalian embryogenesis that consists of an inner cell mass and an outer trophoblast layer.