Stages of Development Flashcards
Stages of development
- Gamete formation
- Fertilization
- Cleavage
- Gastrulation
- Organogenesis
- Growth
Gamete
mature haploid male or female germ cell
Egg components
- Components of a normal somatic cell
- Yolk: Provides energy during development
- Polarity
Polarity
- Animal pole: contains most of the cytoplasm & nucleus
- Vegetal pole: contains most of the yolk
Distribution of yolk in egg
- Isolethical
- Mesolethical
- Telolecthical
- Centrolethical
Isolethical
- Very little yolk evenly distributed through egg
- Typical of placental mammals, tunicates, echinoderms, cephalochordates, and molluscs
Mesolethical
- Moderate amount of yolk concentrated at vegetal pole
- Typical of amphibians
Telolethical
- Abundance of yolk densely concentrated at vegetal pole
- Typical of birds, reptiles, fish, monotremes, some amphibians
Centrolethical
- Large centrally located mass of yolk
- Typical of arthropods
Developmental patterns associated with amount of yolk
Lots of yolk:
* Direct development
* Telolethical eggs
Little yolk:
* Indirect development
* isolecithal, mesolecithal eggs
Fertilization
Gametes unite to form a zygote
Cleavage
- Embryo divides repeatedly without growth
- Occurs more easily in cytoplasm than in yolk
- Egg cell becomes many smaller cells called blastomeres
Holoblastic cleavage
- Complete and equal division of cells
- Isolethical and mesolethical eggs
Meroblastic cleavage
- Restricted to a small area of egg
- Telolethical and centrolethical eggs
Cleavage direction
- Radial cleavage
- Spiral cleavage
Blastula
- Zygote formed at the end of cleavage
- 1 germ layer
Blastocoel
Fluid-filled cavity around which the cells form
Gastrulation
Converts blastula into a 2- to 3-layered embryo
Gastrula
- Embryo at the end of gastrulation
- 2-3 germ layers
Formation of 2nd germ layer
Invagination of blastula
Mesoderm
- 3rd germ layer
- Formed from endoderm between endoderm and ectoderm
Gut cavity (archenteron/gastrocoel)
Internal pouch formed from invagination of blastula
Blastopore
Opening to the gut cavity
Ectoderm
Outer layer of cells (lining of the blastocoel)
Endoderm
Inner layer of cells (lining of the invagination)
Blind gut
Gastrula has one opening
Complete gut
Gastrula has two openings
Coelom
Cavity completely surrounded by mesoderm
Organogenesis
1st event = formation of the nervous system
* Formed from the ectoderm
1st functional organ = heart
* Formed from the mesoderm
Organogenesis takes place during the first 8 weeks
Growth
Longest phase in animal development
