Presentation 3: Development Flashcards
Types of Eggs based on yolk
-. Oligolecithal (Amphioxous and most mammals, very little yolk)
- Isolecithal (Very little yolk + even distribution of yolk)
- Mesolecithal (Moderate amount of yolk i.e. lampreys, amphibians)
- Telolecithal (Large amounts of yolk unevenly throughout egg i.e. most fishes, birds, reptiles, and monotremes)
Oligolecithal
Type of Egg
(Amphioxous and most mammals, very little yolk)
Isolecithal
Type of Egg
(Very little yolk + even distribution of yolk)
Mesolecithal
Type of Egg
(Moderate amount of yolk i.e. lampreys, amphibians)
Telolecithal
Type of Egg
(Large amounts of yolk unevenly throughout egg i.e. most fishes, birds, reptiles, and monotremes)
Types of Cleavage Division
Holoblastic (Oligolecithal eggs, complete division, equal sized blastomeres)
Meroblastic (telolecithal eggs limited cleavage to animal pole, unequal sized blastomere)
Holoblastic
Type of cleavage
Eggs with little or no yolk (i.e. Oligolecithal or isolecithal eggs, total cleavage, equal sized blastomeres)
Ex. amphioxous and most mammals
Meroblastic
Type of Cleavage
Eggs w/ large amounts of yolk (embryo forms thin cap on yolk), telolecithal eggs, cleavage limited to animal pole, unequal sized blastomere)
Ex. most birds, reptiles, and egg laying mammals
Steps of Embryo Development
- Fertilization (result in zygote)
- Morulation = Morula (no inner cavity)
- Blastulation = Blastula (layer of cells surrounding blastocoel / inner cavity)
- Gastrulation => Gastrula (primary germ layers form from blastopore)
Primary Germ Layers
Ectoderm, mesoderm, endoderm
Gastrulation in Oligolecithal
Invagination (blastopore invaginates endoderm cells which form a cavity called an archenteron)
Archenteron
inner cavity that occurs during gastrulation
Gastrulation in Telolecithal eggs
Epiboly and Involution (blastoderm spreads during epiboly and is then involuted at blastopor and folds upwards along edge to form archenteron
Coelom Formation
Telolecithal = Schizocoelous (cavitization of mesoderm)
Oligolecithal = Enterocoely (outpocketings of archenteron
Coelom
cavities in mesoderm
Protostomes vs Deuterostomes gastrulation
Protostomes: blastopore becomes mouth, schizocoelous formation
Deuterostomes: blastopore becomes anus, enterocoelous
Neurulation
Induction of neural tissue
1. Thickening and elongation (neural plate formation with adjacent neural crest and epidermis)
2. Folding (neural crest/groove formation)
3. Convergence (dorsal hinge points fold to produce a tube like structure
4. Fusion (neural tube formed by dorsal most cells on each side of neural tube begin to fuse as well as epidermis
4. Neural crest cells migrate away as fusion is complete
Cleidoic Egg / Amniotic Egg
Chorion, amnion, embryo, allantois, and yolk sac.
Chorion
Outermost part of Amniotic egg
Amnion
Membrane surrounding fetus
Allantois
More posterior side of embryo - accumulates waste
Yolk Sac
More anterior side of embryo, provides nutrients
Mammal Amniotic Egg
Chorion combines w/ uteran wall to form placenta and provide embryo w/ extra nutrients and oxygen.
Umbilical cord wraps around membranes
Phylogeny
Evolutionary history of a species
Ontogony
Lifespan of a single individual
Von Baer’s Laws
- Gen. characters appear before specialized characters
- from gen. characters specialized characters develop
- during development, animal departs from form of others
- Early stages of development in an animal are not like adult stages of other animals, stages do resemble younger stages of animal in lower part of ‘great chain of being’
