isolecithal yolk

embryology

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June 29, 2026

Quick Summary

In embryology, isolecithal yolk refers to eggs that contain a small amount of yolk, which is evenly distributed throughout the egg. This type of yolk distribution is found in invertebrates and most mammals.1

Eggs are classified based on their yolk content and distribution:
* Isolecithal: Small, uniformly distributed yolk.1
* Telolecithal: Abundant yolk concentrated in one hemisphere.1
* Centrolecithal: Yolk massed near the center of the egg.1
* Oligolecithal: A small quantity of evenly distributed yolk (similar to isolecithal).2

The yolk serves as a food source for the developing embryo.2

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yolk
…uniformly distributed yolk are termed isolecithal. This condition occurs in invertebrates and in all but the lowest mammals. Eggs with abundant yolk concentrated in one hemisphere of the egg are termed telolecithal. This occurs in many invertebrates and in all vertebrates lower than marsupial mammals. In arthropods, the yolk is…
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…uniformly distributed yolk are termed isolecithal. This condition occurs in invertebrates and in all but the lowest mammals. Eggs with abundant yolk concentrated in one hemisphere of the egg are termed telolecithal. This occurs in many invertebrates and in all vertebrates lower than marsupial mammals. In arthropods, the yolk is…
Read More