microlecithal

Microlecithal refers to an egg that contains a very small amount of yolk. This type of egg is characteristic of many mammals, including humans, as well as some invertebrates. The small yolk reserves mean that the developing embryo must rely heavily on the mother for nourishment.

In microlecithal eggs, the cytoplasm is relatively evenly distributed, leading to holoblastic cleavage, where the entire egg divides. This contrasts with eggs that have a large amount of yolk, which can impede or alter the pattern of cleavage. The yolk granules in microlecithal eggs are typically scattered throughout the egg.

The presence of minimal yolk is an evolutionary adaptation that allows for more efficient internal development within the mother. The yolk's primary role is to provide nutrients for the early stages of embryonic development until a placenta or other nourishing structure is established. The limited yolk is therefore not sufficient to support the entire embryonic development on its own. This characteristic is a key feature in classifying egg types based on their yolk content.