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Introduction to. EMBRYOLOGY. 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. Types of Egg Laying/Birth.
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Introduction to EMBRYOLOGY
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
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
Invagination vs. Evagination • Invagination: movement of cells or tissues inward • Evagination: movement of cells or tissues outward
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
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
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