Lesson 4 - Early Craniate Morphogenesis Flashcards
bilaterally symmetrical chordates with indeterminate cleavage with mouth not arising from blastopore
deuterostomes
closes relatives of chordates
- Hemichordates
- Echinoderms
- believed to be closer relatives of chordates but still being debated on
- believed to have branched off
Cephalochordates or Tunicates
show resemblance to each other in neuroanatomy and biochemistry
- cephalochordates
- vertebrates
Egg types: amount of yolk
- microlecithal
- mesolecithal
- macrolecithal
- very little yolk
- amphioxus, therian mammals
microlecithal
microlecithal example
- amphioxus
- therian mammals
- moderate amount of yolk
- amphibians
mesolecithal
mesolecithal example
amphibians
- large amount of yolk
- reptiles, monotremes
macrolecithal
macrolecithal example
- reptiles
- monotremes
Egg types: yolk distribution
- isolecithal
- telolecithal
- yolk is evenly distributed in the cytoplasm
- seen in microlecithal egg
isolecithal
where is isolecithal seen
microlecithal egg
- yolk is concentrated in one pole (vegetal pole)
- seen in mesolecithal and macrolecithal eggs
- opposite pole contains the nucleus and relatively yolk free cytoplasm
telolecithal
where is telolecithal seen
- mesolecithal
- macrolecithal eggs
two pole in telolecithal
- vegetal pole
- animal pole
where yolk is concentrated
vegetal pole
opposite pole containing the nucleus and relatively yolk free cytoplasm
animal pole
Ways offsprings are produced by interal fertilization
- oviparity
- viviparity
- animals that lay eggs (spawn)
- eggs contain sufficient amount of yolk and albumen to support the development into a free-living organism that is able to take food orally
oviparous
fully formed when hatched
(birds)
oviparous macrolecithal
example of fully formed when hatched
birds
young hatch in larval stage
(frog)
oviparous mesolecithal
example of young hatch in larval stage
frog
young hatch in a free-living and self-nourising stage
(amphioxus)
oviparous microlecithal
example of young hatch in a free-living and self-nourising stage
amphioxus
animals that give birth to offsprings
viviparous
different types of viviparity
- ovoviviparity
- euviviparity
- mother provides only protection and oxygen
- nourishment stored in the egg
ovoviviparity
example of ovoviviparous animal
spiny dogfish shark
embryos are dependent on maternal tissues for all nourishment, oxygen, excretion of wate products of metabolism
euviviparity
- egg may be fertilized and the young may develop in the ovarian follicle or ovarian cavity
- trophotaeniae
viviparous teleosts
where do viviparous teleosts develop
- ovarian follicle or
- ovarian cavity
- External, umbilical cord-like structure present in members of the family Goodeidae and some other fish groups responsible for transfer of nutrients between an adult female and her internally-developing young.
- May still be attached to fry at birth
trophotaenia
meaning of word trophotaenia
trophe = nutrition
taenia = band
Different types of fertilization
- internal fertilization
- external fertilization
- fertilization takes place within the body of the female (viviparous craniates)
- intromittent organ is needed to introduce sperm into the female reproductive tract
- eggs are covered by impenetrable shell before being extruded (reptiles)
internal fertilization
what is needed in internal fertilization in order for the sperm to be introduced into the female reproductive tract
intromittent organ
- millions of sperm cells are shed over the eggs as the eggs are being extruded
- oviparous fishes, frogs, and toads
external fertilization
example of external fertilization
oviparous fishes, frogs, toads
describes sexually reproducing fishes that develop mature gonads containing oocytes and spermatozoa
Hermaphroditism
considerably different from juveniles and adults
larvae
Stages in Early Development
- gamete formation
- fertilization
- cleavage
- gastrulation
- organ formation
- growth, tissue specialization
- repeated mitotic cell division of the zygote initiated by the union of two mature sex cells or gametes
- embryo experience little or no growth in size
cleavage or segmentation
- formed during cleavage
- multicelled and hollow sphere
blastula
cells resulting from the early cleavage division of the ovum
blastomeres
fluid filled cavity in a blastula
blastocoele
cells of the blastula form an epithelial (covering) layer
blastoderm
Types of Cleavage
- holoblastic cleavage
- meroblastic cleavage
- discoidal cleavage
- entire egg undergoes cellularization, and yolk platelets are either absent (e.g., in mammals) or present as cytoplasmic inclusions that partition among cells (e.g., in amphibians)
- mitotic furrow pass through the entire zygote from animal to vegetal pole
holoblastic cleavage
mitotic furrow in holoblastic cleavage
pass through the entire zygote from animal to vegetal pole
holoblastic cleavage in microlecithal eggs
blastomeres are approximately of equal size
holoblastic cleavage in mesolecithal eggs
yolk laden cells in vegetal pole divide more slowly and are larger
- where yolk is plentiful macrolecithal)
- cleavage furrows form, but do not progress into the yolk.
- mitotic furrow is slowed and only a portion of the cytoplasm in the animal pole is cleaved
- Species that exhibit this type of cleavage are birds, insects, fish, and reptiles
meroblastic cleavage
mitotic furrow in meroblastic cleavage
- slowed
- only a portion of the cytoplasm in the animal pole is cleaved
- extensive yolk material at the vegetal pole remains undivided by mitotic furrows
- cleavage restricted to a cap of dividing cells at the animal pole
discoidal cleavage
mitotic furrow in discoidal cleavage
do not divide extensive yolk material at vegetal pole
where is discoidal cleavage restricter to
cap of dividing cells at animal pole
Mechanisms of cleavage
- localized expansion of cortex
- increased stiffness of the cortical cytoplasm
- increased tangential force activity in the cortex
- contractile nature of regions near the cortex
- formation of new cell membrane from the subcortical sytoplasm
cleavage follows __
fertilization
when is the cleavage called blastula
after it produced over 100 blastomeres
- continued cleavage produces this
- it is a microscopic ball or cluster of cells formed through cell division very early in the embryonic development that occurs after the formation of a zygote through fertilization but before the blastocyst stage.
morula
no. of cells in morula
16 cells