5. Development Flashcards
Importance of Developmental studies
Evidence for common descent
Helps with construction of phylogenies
Ontogeny
Developmental history of an individual throughout its life
Ernst Haeckel
“Ontogeny recapitulates phylogeny”
Suggested that the developmental stage represented the adult stage of its evolutionary history
Key events in animal development
- Gamete formation
- Fertilization
- Cleavage
- Gastrulation
- Organogenesis
- Growth
Egg
An ovum
Ovum
Female reproductive or germ cell
Germ cell
Haploid cell whose fertilization by one of the opposite kind produces a diploid zygote
Gamete
A mature haploid sex cell, egg or sperm
Egg’s polarity
Animal Pole - Mostly cytoplasm
Vegetal Pole - Mostly yolk
Isolecithal
Very little yolk
Evenly distributed
- Placental animals
- Echinoderms, tunicates, cephalochordates, molluscs
Mesolecithal
Moderate amount of yolk concentrated at vegetal pole
- Amphibians
Telolecithal
Abundance of yolk densely at vegetal pole
- Birds, reptiles, fish, monotremes, some amphibians
Centrolecithal
Large centrally located mass of yolk
- Arthropods
Development of telolecithal eggs
Egg to miniature adult
Development of isolecithal/mesolecithal eggs
Larval stage capable of feeding itself
Metamorphosis to reach adult
- exceptions: mammals
Holoblastic cleavage
Complete and approximately equal divisions of cells
- isolecithal, mesolecithal
Meroblastic cleavage
Restricted to small area of egg
- Telolecithal, Centrolecithal
Direction of cleavage
Spiral / Radial
Gastrulation
Converts spherical blastula into two or three layered embryo
Germ layers
Layers that form during gastrulation
Gastrulation process
- One side of the blastula bends inward in a process called invagination
- Internal pouch formed is the gut cavity (archenteron or gastrocoel)
* The opening to the gut cavity is the blastopore - A second opening forms, forming a gut tube
- Third layer forms from endoderm
Gut Cavity’s names
Archenteron, Gastrocoel
Outer Layer of Blastula
Ectoderm
Inner Layer of Blastula
Endoderm
