Holoblastic

Holoblastic is a type of cleavage that occurs during the early stages of embryonic development. This process is characterized by the division of the entire egg into smaller cells, known as blastomeres. Holoblastic cleavage is common in species with little or no yolk in their eggs, such as mammals and sea urchins.

Types of Holoblastic Cleavage

There are two main types of holoblastic cleavage: equal and unequal.

Equal Holoblastic Cleavage

In equal holoblastic cleavage, each division of the egg results in blastomeres of approximately the same size. This type of cleavage is common in species with isolecithal eggs, which have a uniform distribution of yolk.

Unequal Holoblastic Cleavage

Unequal holoblastic cleavage results in blastomeres of different sizes. This type of cleavage is common in species with telolecithal eggs, which have a concentrated distribution of yolk. The larger blastomeres contain more yolk, while the smaller blastomeres contain less.

Comparison with Meroblastic Cleavage

Holoblastic cleavage differs from meroblastic cleavage, another type of embryonic cell division. In meroblastic cleavage, only a portion of the egg divides, due to the presence of a large amount of yolk. This type of cleavage is common in species with heavily yolked eggs, such as birds and reptiles.

See Also

• Cleavage (embryology)
• Blastomere
• Meroblastic cleavage
• Yolk

References

Holoblastic Resources
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