What is the Difference Between Radial and Spiral Cleavage?

Radial and spiral cleavage are two types of holoblastic cleavage that occur in early embryonic development, depending on the amount of yolk in the egg. The main differences between radial and spiral cleavage are:

• Location: Radial cleavage is found in deuterostomes, while spiral cleavage is found in protostomes.
• Cell Arrangement: In radial cleavage, the division planes are at 90-degree angles, resulting in daughter cells that are located exactly on top of one another. In contrast, spiral cleavage has division planes that are not at 90-degree angles, and the resulting blastomeres are not aligned directly over or beside one another.
• Spatial Arrangement: Radial cleavage causes the developing embryo to divide along the axis of the embryo's polarity, while spiral cleavage involves the division of cells in an irregular manner.

Both radial and spiral cleavage involve blastomeres, which are cells involved in the embryonic stage of development. These blastomeres are arranged in two tiers: the upper and lower tiers. However, the fate of the blastopore, which determines the type of cleavage (radial or spiral), also determines the location and function of the developed structure. In protostomes, the blastopore becomes the mouth, while in deuterostomes, the blastopore becomes the anus.

Comparative Table: Radial vs Spiral Cleavage

Here is a table comparing radial and spiral cleavage:

Both radial and spiral cleavages are holoblastic, meaning the division planes cut completely through the cells during cytokinesis. The differences in the cleavage patterns result in different developmental outcomes for the daughter cells. In spiral cleavage, the early embryonic cells retain the capacity to develop into a complete embryo, making the blastomeres qualitatively totipotent. In contrast, most deuterostomes exhibit indeterminate cleavage, where the early embryonic cells develop into determinate cells, programmed to become a specific type of cell.