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Understanding Vertebrate Embryology: Egg Types, Development, and Key Terminology

This overview of vertebrate embryology explores various egg types, including microlecithal, macrolecithal, mesolecithal, isolecithal, and telolecithal eggs distinguished by yolk quantity and distribution. It covers reproductive strategies like oviparous, viviparous, and ovoviviparous births. Key processes such as invagination and evagination are explained, alongside meiosis in gamete formation. Important embryological terms are defined, including diploid, morula, blastula, and somites, providing clarity on the essential stages of embryonic development.

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Understanding Vertebrate Embryology: Egg Types, Development, and Key Terminology

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  1. Introduction to EMBRYOLOGY

  2. Vertebrate Eggs • Microlecithal: very little yolk • Macrolecithal: massive amount of yolk • Mesolecithal: moderate amounts of yolk • Isolecithal: even distribution of yolk • Telolecithal: cytoplasm and yolk are on opposite poles of egg

  3. Types of Egg Laying/Birth • Oviparous: lay eggs • Viviparous: live birth (with placenta) • Ovoviviparous: live birth; no placenta (dogfish shark) • Euviviparous: nourishment must be supplied constantly by mother

  4. Invagination vs. Evagination • Invagination: movement of cells or tissues inward • Evagination: movement of cells or tissues outward

  5. Meiosis • Forms gametes • Reduces number of chromosomes by half • When two gametes join, normal number of chromosomes are restored • Gametes are HAPLOID (n) • Zygote: fertilized egg

  6. Embryology Terms to Know • Diploid: whole number of chromosomes (2n) • Morula: Solid mass of 16 cells • Clevage: split in cell • Blastula: hollow ball of cells • Blastocoel: hollow part of blastula • Gastrocoel: hollow space after invagination

  7. More Terms to Know • Primitive Streak: develop of chick • Somites: blocks of mesoderm that form structures and organs (tells the age of embryo) • Henson’s Node: knot from which the notochord grows

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