Tree Thinking and Development Flashcards
Which group makes up the largest percentage of vertebrates?
Fishes
How are phylogenetic trees made?
By comparing morphology and gene sequences of organisms. The most different species becomes the outgroup
What is the principle of parsimony?
Minimizing the number of evolutionary events
What is the benefit of W-shaped myomeres?
Allows for better and more precise swimming movements
What does the presence of chemosensation in the head imply?
A predatory lifestyle
Why can’t mammals be too small?
They are homeothermic endotherms, so being tiny increases the SA:V ratio and it becomes very expensive to maintain body temperature. RMR goes up the smaller you are.
Are vertebrates protostomes or deuterostomes?
Deuterostomes
What is a monophyletic tree?
It includes the MRCA and all clades
What is a paraphyletic tree?
It includes the MRCA but excludes some clades, “cherry-picks”
What is a polyphyletic tree?
Does not include MRCA, “cherry-picks”
What are chordate synapomorphies?
Notochord
Dorsal hollow neural tube
Endostyle
Postanal tail with simple fin
What is the function of the endostyle?
It has a role in iodine acquisition and hormone/metabolism regulation
What are chordate apomorphies?
V-shaped myomeres
Unmuscularized pharynx
Pharyngeal slit
Pulsating blood vessels, no true heart
What are vertebrate synapomorphies?
Cranium
Spinal cord
Notochord
Vertebrae
W-shaped myomeres
Postanal tail with fin rays
Thyroid
What are vertebrate apomorphies?
Gill arch with gills
Muscularized pharynx
Multichambered heart
Muscularized gut
Mineralized tissues
Why is development important to study?
Developmental pathways tend to be conserved among phylogenies
List the steps of development in order of occurance
- Gastrulation
- Neurulation
- Division of mesoderm
- Somite formation
- Form body cavities
- Neural crest migration
Describe the differences in gastrulation between fishes and amphibians vs. birds, reptiles, and mammals
Fishes and amphibians: Start as a sphere, invaginates at dorsal lip of the blastopore
Birds, reptiles, and mammals: Start as a plate and invaginate at the primitive streak
Describe the differences in neurulation between fishes and amphibians vs. birds, reptiles, and mammals
The general steps are the same, so no key differences
Describe the process of neurulation
The notochord induces the neural plate and neural folds to form. As the notochord moves downwards (ventrally), the neural plate invaginates to form the neurocoel. The neural folds meet in the middle and fuse, forming the epidermis
What type of cells do neural folds contain?
Neural crest cells
What tissues does the ectoderm make?
Skin, feathers, scales, teeth, posterior digestive system, and the brain and spinal cord
What tissues does the mesoderm make?
Dermis, skeleton, respiratory and circulatory systems, urinary system, reproductive system, and skeletal muscle
What tissues does the endoderm make?
Respiratory and circulatory systems, urinary system, reproductive system, and anterior digestive system
What are the three divisions of the mesoderm from innermost to outermost?
Paraxial (somitic) mesoderm, intermediate mesoderm, and lateral plate mesoderm
What does the paraxial (somitic) mesoderm split into?
Head and somites
What are somites?
Muscle and connective tissue, Blocks of mesoderm that determine the migratory path of neural crest cells
What do somites divide into?
Sclerotome (cartilage)
Syndotome (tendons)
Myotome (skeletal muscle)
Endothelial cells
Dermatome (dermis, skeletal muscle)
What does the intermediate mesoderm divide into?
Kidney
Gonads
What tissues does the lateral plate mesoderm divide into?
Splanchnic (circulatory system, visceral organs)
Somatic (body cavity, pelvis, limb bones, body wall)
Extra-embryonic (not produced in every species
Which three tissues are formed following somite formation?
Dermatome, myotome, sclerotome in that order
Describe the general process of the formation of body cavities
The lateral plate mesoderm folds inwards (ventrally) until the two ends meet. The somatic and splanchnic layers form around the coelom (cavity). Between these two cavities is the endoderm, which forms the gut. The dermatome, myotome, and sclerotome form near the neural tube
Describe neural crest migration
After body cavities form, the neural crest cells formed during neurulation migrate outwards
What is neurulation?
The development of the neural tube
What are some key neural crest derivatives?
The arches (mandibular, hyoid, carotid, and branchial arches 1-5), the pre-mandibular domain
What are homeobox domains?
Conserved 180bp segments of DNA encoded in homeobox genes
What are Hox genes?
A subset of homeobox genes that organize the body plan using homeobox-controlled transcription factors
What is the purpose of Hox genes?
They allow for certain genes to be repeated (limbs, teeth, digits), which creates diversity
Which arch forms the upper and lower jaws?
Mandibular
Branchial arches 1-5 resulted from:
Hox gene expression
What tissue layer is the neural plate made from and what does it become?
Made from ectoderm and becomes the nervous system
What will the chordamesoderm form?
The notochord
What components made up the Neurectoderm?
-Neural crest and neurogenic placodes
-Neural tube
What is the 4th germ layer in vertebrates and what does it produce?
Neural crest*** key thing that makes vertebrates different
-pigment cells
-head structures (dentine in teeth)
-Nerve ganglia
-Some parts of the heart
What does the nasal placode give rise to?
Sensory organs
What is the mineral in mineralized connective tissue?
Hydroxyapatite
What are the mineralized connective tissues? (6)
-Enamel (ameloblasts)
-Enameloid (ameloblasts and odontoblasts)
-Dentine (odontoblasts)
-Bone
-Mineralized cartilage
-Cementum
What are the jaws of Gnathostomes homologous to in Cyclostomes?
The first gill arch
True/False? The dermatocranium is present in Chondrichthyes
False
What is the space lateral to the gill arch?
The opercular cavity
Define synapomorphy
A shared derived character. Present in two or more taxa and are inherited from their most recent common ancestor. Synapomorphies are key in identifying evolutionary relationships. For example, the presence of a vertebral column is a synapomorphy of all vertebrates.
Define apomorphy
A derived character (traits that are unique to a particular group and were not present in its ancestral form). Can be specific to a single species or group, and it may not necessarily be shared among other taxa
