Vertebrate Origins - Development Flashcards
Weeks 1-8 of development is called what?
The embryo
Weeks 9-38 are called what?
Fetal Period
What are the germ layers of the embryonic disk?
Ectoderm, mesoderm, endoderm
What does gastrulation lead to?
The rotation of the embryo, cranial pulse from node = notochord, which is covered by ectoderm. and enters to elongation phase
What are the two parts of the lateral plate?
Paraxial and Intermediate Mesoderm
What does the paraxial mesoderm proliferate?
Divides into somites:
Sclerotome, dermatome, myotome
Wat happens to the sclerotome?
- migrates to surround the notochord and spinal cord (neural tube)
- cartilage and bone of mesodermal axial skeleton
- vertebrae, ribs, occiput of skull
Parietal Mesoderm
Gives way to body wall including the limb buds
visceral Mesoderm
Muscle wall of gut and parts of the circulatory system
Crown Vertebrata (563) is defined by the split between
Cyclostomata and Gnathostomata
Crown Cyclostomata is defined by the split between
Hagfish and Lamprey
What are hagfish
Deep marine, scaleless with an eel-like form. They have a single medial nostril, paired eye spots, pharyngeal slits
what are some characteristics of Lampreys
Freshwater, dorsal and caudal fin, 7 gill slits
Within Crown Vertebrata, there is increased genetic complexity due to….
Genome Duplications
Teleost fish, Gnathostome, and vertebrate stem lineages
Duplications created genetic redundancy - paralogs
What are paralogs?
Copies of the same gene in same individual
What are orthologs?
Copies of the same gene in differnt lineages
What is the most common outcome from drift?
Loss!
What are the different evolutionary possibilities?
Loss, neofunctionalization, complementation, and subfunctionalization
What is neofunctionalization?
It’s when novel sequences produce novel function
- positive selection creates innovation
- different regulatory genome of existing structural genes
What is subfunctionalization
Ancestral function(s) conserved, but is divided between paralogs
- modularity
What is complementation?
Think genetics!
Both paralogs are needed to maintain ancestral function
What are some vertebrate synapomorphies?
1) Neural crest = ectomesenchyme, which is highly motile and multipotent
- connective tissue = neural crest & muscle = mesoderm
A) Head and Branchial Skeleton (cartilage)
- neurocranium, trabeculae, optic capsule, support elaborate gill structure
- PNS, ANS (not PS nuclei in brain), adrenal gland, and melanocytes
2) Placodes
- localized thickenings of surface ectoderm
- normally paired
3) Sclerotome
- derived vertebral column
- Lamprey: dorsal elements only, lateral to DHNC, cartilagenous
- Hagfish: ventral, similar genes as gnathostome sclerotome
What are the differnt kinds of placodes?
Sensory
- lens (no sensory epithelium), otic, olfactory, lateral line
Neurogenic
- sensory - neurons to ganglia of CN 5,7,9, 10
What does Pan-Vertebrata include?
From bottom to top
Olfactores - Urochordata
Gills!
Yunnanozoa
Loss of atrium
Pikaia
Neural crest
Cartilagenous skeleton, eyes, ears, midline nostril
Haikouchthys
Vertebrata
