What unique cleavage pattern is observed in frog embryos?

The unique cleavage pattern observed in frog embryos is uneven holoblastic cleavage. This type of cleavage refers to the complete division of the egg during the early stages of embryonic development, but it is characterized by unequal sizes of the resulting blastomeres. In frogs, the distribution of yolk in the egg causes the cleavage furrows to form differently across the embryo, leading to smaller cells in the animal pole (where the nucleus is concentrated) and larger cells in the vegetal pole (where the yolk is abundant).

This pattern is significant because it influences subsequent developmental processes, including the distribution of cells that give rise to various tissues and organs. In contrast, other cleavage patterns like radial cleavage typically involve equal-sized blastomeres and are more common in other organisms, such as echinoderms. Meroblastic cleavage refers to partial division often seen in organisms with a large amount of yolk, such as birds, while complete cleavage generally suggests equal division, which is not characteristic of frogs.