Early Craniate Morphogenesis Why study this material? Morphology

What is Life History? Distinct periods or times? How should we refer to them? generate list(s) on board

Craniate Eggs Types of eggs: * distribution of yolk… found in placental mammals and amphioxus * distribution of yolk concentrated at the vegetal pole… found in lampreys, bony fish, amphibians * eggs… found in marine lampreys, cartilaginous fish, reptiles, monotremes frog.jpg

Craniate Eggs Oviparity & Viviparity: Animals that “lay” their eggs are considered _________________. Animals that give birth are considered _________________. If the embryo could develop without maternal tissue then _____________, while dependent strategies are __________________ No viviparous …

Craniate Eggs Viviparity: hamburg.de/zim/herpe/bilder/Ichthyophis_Embryo.jpg

Craniate Eggs Fertilization: ________________________mode s exist In which type of “–parity” are eggs by necessity internally fertilized? Usually external fertilization requires … Urodeles (salamanders) may use … ae/triturus/cristatus/triturus_cristatus_mazzei.jpg

Early Development Cleavage and the blastula: As fertilized egg cells divide this is called _____________. What happens to cell size initially? Hollow sphere is called the ________ and it contains a hollow space… the _____________. Excessive yolk impedes cell division… such that a ______________ develops on an otherwise undivided yolk. What taxonomic group(s) would utilize this mode?

Early Development Let’s review what we can infer since we know this is “Chordate” development… What type of cleavage pattern? What does the 1 st opening become? How many germ layers do we have?

Early Development _______________ is the process in which 3 primitive germ layers are formed Amphioxous eggs lack yolk and provide a clear picture Involution of blastula Resultant opening is the ______________________

Early Development Mesoderm forms from the ___________ and then creates pouches (coelomic or mesodermal) Lateral/superficial layer becomes ___________________ Inner/deep layer becomes ___________________ What becomes of the ectoderm? How about the endoderm?

Early Development Gastrulation: Frog – because the yolk cells are slow… involution is delayed. Consequently, slightly different process accomplishes same ends. Lateral mesoderm moves in from sides and ventral area of blastopore heading for the head.

Early Development Gastrulation: Chick – Special consideration required when we have a marolecithal egg. Blastoderm (epiblast and hypoblast) ______________ continues around the yolk to become part of the yolk sac ______________ has cells migrating inward that become endoderm Cells destined to become the mesoderm migrate in between the other 2 “derms”

Early Development What regulates differentiation of these cells into various germs, derms, tissues and organs? Organizer area _________________ (sonic hedgehog gene) Proteins involved in signaling called ____________________ Defective homeotic genes can have severe developmental consequences… opup/r7_spinabifida.jpg

Early Development What is the fate of the different “derms”?

Germ Layers Placental mammals have varying approaches to gastrulation However, generally a ______________forms __________develop resulting in a __________________ Neural folds unite forming a _______________ Process called ____________

Extraembryonic Membranes Extraembryonic membranes include:

Extraembryonic Membranes __________is a highly vascular membrane that surrounds the yolk. Empties into the … Can secrete … Can serve as … Can absorb nutrients from mother… functions as a simple yolk sac placenta or a “__________________” sources/Pictures/embryo-1-wk.JPG

Extraembryonic Membranes Reptiles and mammals develop inside 2 sacs… ___________surrounds the embryo ___________surrounds the amnion and the yolk sac Important feature that allows eggs to be laid on land (with less dependence on water) Amniotic fluid surrounds the embryo and is contained by the amnion Where does this water come from?

Extraembryonic Membranes ___________ is an evagination of the ___________ Communicates with the inner surface of the chorion forming the … Reptiles and monotremes aids in … In most mammals serves as a membrane of the placenta… transferring … Base of this sac becomes the …

Extraembryonic Membranes ___________ generally is any place embryonic and maternal tissues come together for exchange More specifically/restricted definition… organ containing highly vascular region of extraembryonic membrane in communication with highly vascular region of maternal tissue

Extraembryonic Membranes Placentas can have a simple communication with maternal tissue… ___________________ Or They can have chorionic villi that invade endometrium and pull part of this lining off with birth… __________________ Villi can be positioned variously on the chorion _placenta_uterine_side.jpg/799px-Human_placenta_uterine_side.jpg