Key Difference – Telolecithal vs Centrolecithal Egg
There are different types of eggs (ova), and based upon the distribution of the egg yolk, eggs are categorized as Telolecithal and Centrolecithal egg. The key difference between the Telolecithal and Centrolecithal eggs is based on the distribution of the yolk in the cytoplasm of the ovum. In telolecithal egg, the yolk is unevenly distributed in the ovum cytoplasm. In centrolecithal egg, the yolk is concentrated to the center of the ovum cytoplasm.
CONTENTS
1. Overview and Key Difference
2. What is Telolecithal Egg
3. What is Centrolecithal Egg
4. Similarities Between Telolecithal and Centrolecithal Egg
5. Side by Side Comparison – Telolecithal vs Centrolecithal Egg in Tabular Form
6. Summary
What is Telolecithal Egg?
Telolecithal eggs are usually present in fish, amphibians, reptiles, and birds. These eggs contain an egg yolk that is distributed throughout the cytoplasm of the ovum. Therefore, the yolk is said to be distributed unevenly. Telolecithal eggs are mainly composed of two main poles. The vegetal pole is the area in which the yolk is densely distributed. The distribution of the yolk is less dense in animal pole. In Telolecithal eggs, the yolk forms large granules that are known as the yolk platelets. They are oval in shape and flattened structures.
Figure 01: Telolecithal Eggs of Fish
During the cleavage step, during embryonic development, the Telolecithal eggs undergo discoidal cleavage giving rise to the blastocoel. Here, the cytoplasm fails to cleave completely.
What is Centrolecithal Egg?
Centrolecithal eggs are mainly present in insects and some arthropods. In centrolecithal eggs, the cytoplasm is concentrated to the middle of the ovum. Therefore, the cytoplasm of the ovum is restricted to a thin peripheral layer. In centrolecithal eggs, most of the yolk is liquid, but a solid part can also be observed. This is known as the yolk sphere.
Figure 02: Centrolecithal Eggs of Insects
During the cleavage step, the Centrolecithal eggs undergo superficial cleavage. The cleavage is limited to the thin cytoplasm layer. Therefore, the egg fails to cleave.
What are the Similarities Between Telolecithal and Centrolecithal Egg?
- Both Telolecithal and Centrolecithal eggs are termed based on the distribution of the egg yolk.
- The egg yolk in both eggs are involved in providing energy for the maintenance of the embryonic development.
What is the Difference Between Telolecithal and Centrolecithal Egg?
Telolecithal vs Centrolecithal Egg |
|
| In telolecithal eggs, the yolk is unevenly distributed in the ovum cytoplasm. | In centrolecithal eggs, the yolk is concentrated in the center of the cytoplasm of the ovum cytoplasm. |
| Distribution of the Egg Yolk | |
| Throughout the cytoplasm of the ovum, along the vegetal pole egg yolk is distributed. | Egg yolk is concentrated in the center of the cytoplasm of the ovum in centrolecithal egg. |
| Texture of the Yolk | |
| Yolk is present as large granules known as the yolk platelets in telolecithal egg. | Yolk is mostly liquid, but some solid parts are present that are known as yolk spheres in centrolecithal egg. |
| Presence of the Vegetal Pole and Animal Pole | |
| Vegetal pole and animal pole are present in telolecithal egg. | Vegetal pole and animal pole are absent in centrolecithal egg. |
| Distribution of the Cytoplasm in the Ovum | |
| Uneven distribution of the cytoplasm of the ovum is seen in telolecithal egg. | The cytoplasm forms a thin lining in the periphery of the cell in centrolecithal egg. |
| Cleavage | |
| Discoidal cleavage of the egg giving rise to the blastocoels is seen in the telolecithal egg. | Superficial cleavage is observed in the centrolecithal egg. |
| Examples | |
| Fish, reptiles, amphibians, and birds are having by the telolecithal egg. | Insects and some arthropods have the centrolecithal egg. |
Summary – Telolecithal vs Centrolecithal Egg
Telolecithal and Centrolecithal eggs are two types of eggs categorized based on the distribution of their egg yolk. If an uneven distribution of egg yolk is observed, it is referred to as a Telolecithal egg. If the egg yolk is concentrated to the center and a thin peripheral cytoplasm is observed, those eggs are referred to as Centrolecithal eggs. This is the difference between telolecithal and centrolecithal egg.
Reference:
1.Cullis, Devante. “Cleavage Is the First Phase of Embryonic Development.” SlidePlayer, 29 June 2017. Available here
2.“Eggs Present in the Ovum: Microlecithal, Mesolecithal and Macrolecithal Eggs.” Biology Discussion, 27 Aug. 2015. Available here
Image Courtesy:
1.’DiskuslaichaS’By M. Kraus (= user Fg-tiger) – fotografiert von M. Kraus, (CC BY-SA 2.0 de) via Commons Wikimedia
2.’2012-05-24 15-14-51-insect-eggs’By Thomas Bresson – Own work, (CC BY 3.0) via Commons Wikimedia