Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
28 Cards in this Set
- Front
- Back
Ontogeny
|
history of life of an organism: its cycle of development, growth & maturation
|
|
Heterochrony
|
# Define
* change in relative rate of development of characters in phylogeny * trait may have developed faster or slower in ancestral taxon * displacement of a feature in an organism relative to the time that feature appeared in an ancestor # Significance * easy way to achieve major evolutionary change (fewer genes altered) |
|
Paedomorphosis
|
#
# loss of 1 or more ontogenetic stage(s) # larval or immature features of ancestors become adult characters # i.e. the retention of a more flexible juvenile morphology # Methods * speed development of reproductive organs so sexually mature "juveniles" form * delay or slow down development of somatic organs; its sexually mature but some other "somatic" traits look unfinished |
|
Peramorphosis
|
* Define
* "old looking" * addition of new developmental stage(s) in descendants * increase in specialized complexity of adult * Methods o somatic structure appears early & develops fast + Example - overdeveloped/huge Irish elk antlers o period of ontogeny extended; new structures can be added |
|
Egg Yolk: Evolutionary Trends
|
* vertebrates, in general, have larger yolks in vertebrates than ancestral invertebrates or other Chordates, this correlates to the larger body sizes of many vertebrates
* microlecithal eggs are secondarily derived in therian mammals; i.e. ancestral trait was lost in most vertebrates, but "reacquired" in therian mammals |
|
Types of Eggs (3)
|
# Variation - within each category listed below, the proportion of yolk varies with body size, numbers of offspring, development patterns
# See Taxonomic variation in table below # Microlecithal (Oligolecithal) - little yolk in egg, very small * Non Craniate Taxa - Echinodermata; Urochordata, Cephalochordata o # Mesolecithal - moderate amount of yolk # Macrolecithal - large amount of yolk |
|
Zygote - single cell after fertilization
A. Yolk Distribution * Isolecithal? Telolecithal? |
Isolecithal
* Define - yolk divided "equally" into all future cells; seen in microlecithal eggs * Taxa - Theria, Urochordata & Cephalochordata Telolecithal * Define - yolk concentrated at vegetal pole; little yolk gets in cells at animal pole * Taxa - all vertebrates with mesolecithal & macrolecithal eggs |
|
Cleavage
* Holoblastic? |
complete cleavage through animal & vegetal poles
* possible only in eggs with little yolk (i.e. microlecithal or mesolecithal eggs) |
|
Cleavage: Meroblastic?
|
incomplete, only animal pole divides into cells, yolk doesn't
|
|
Cleavage: Discoidal?
|
an extreme form of meroblastic cleavage
* very tiny cells are produced at animal pole; huge yolk mass |
|
Evenness of Cell Size
|
# Equal - all cells are equal in size & yolk content
# Unequal- animal pole cells are small & vegetal pole (yolk) cells larger * Pattern o mesolecithal (yolk cells are larger than animal pole cells) o macrolecithal (yolk mass does not divide at all) |
|
Blastula?
|
Define - hollow ball of cells forms as cleavage continues
|
|
Blastula Formation: Mesolecithal (Amphibian) Pattern
|
# Blastomeres
* newly formed cells of this hollow ball * upper "animal" cells, smaller than lower "yolk" filled cells, large # Blastocoel - large hollow cavity inside blastomeres |
|
Blastula Formation: Macrolecithal (Aves & most Amniotes) Pattern
|
Blastodisc
* no true blastula forms * small cluster of tiny, (animal pole cells) on top of solid mass of yolk form blastodisc * separates into top & bottom layers or sheets of cells with a narrow blastocoel space o Epiblast = upper layer source of all 3 germ layers o Hypoblast = lower layer; will be displaced by endoderm |
|
Gastrula
A. Major Events |
# Gut formation - archenteron (lining made of endoderm)
# Embryo becomes bilaterally symmetrical, elongated & cephalized * gastrulation may overlap with neurulation # Formation of 3 germ layers - endoderm, ectoderm & mesoderm * ectoderm cells are the exterior layer of cells * endoderm cells migrate inside "above" yolk cells * mesoderm cells form a layer between endoderm & ectoderm layers |
|
Extra Germ Layer Terminology
Mesenchyme? Ectomesenchyme? |
o mesenchyme - separate mesoderm cells surrounded by extracellular matrix (may be found in embryos & adults)
o ectomesenchyme - neural crest cells that invade mesoderm layer during development |
|
Gastrulation: Mesolecithal (Lissamphibian) Pattern
|
B. Mesolecithal (Lissamphibian) Pattern
* formation of a cleft or dorsal lip * at this location, cells move/migrate over blastula & then migrate inside blastocoel * opening enlarges into circular blastopore - this opening will become adult anus * animal pole cells overgrow the yolk filled cells & yolk cells fill the blastopore as a yolk plug * blastocoel ultimately disappears * archenteron or small, primitive gut (enteron) forms & is filled with yolk |
|
Gastrulation: Macrolecithal (bird) Pattern
|
* primitive streak forms an anterior-posterior zone in midline of blastodisc
* anterior-most point of streak is called Hensen's node * primitive streak & Hensen's node are homologous to blastopore * epiblast cells turn inward & migrate laterally & anteriorly to form mesoderm & endoderm * archenteron closes off slowly as embryo "lifts" off of yolk; stays attached to yolk via stalk |
|
Coelom Formation:
Enterocelous vs Modified Enterocoelous |
Enterocoelous Coelom Formation
* Taxa - primitive deuterostomes (Echinoderms, primitive chordates) & anterior region of lamprey * Method - mesoderm folds inward as pockets off of endoderm Modified Enterocoelous * Taxa - most vertebrates (including posterior region of lamprey) * Method o superficially - solid block of mesoderm splits open to form cavity o mimics shizocoelous coelom formation of protostomes - annelids, arthropods... o differs from "true" schizocoely because mesoderm/endoderm in vertebrates are NOT distinct germ layers at the start of gastrulation |
|
Functions of Coelom
|
# hollow body cavities lined with mesoderm
# tube (gut) within a tube (coelom space) * membranes that line cavity produce serous fluids that provide lubrication for organ movement * frees organs from linkage to movement of trunk |
|
Typical Neurulation Events
|
# Timing - formation of the nervous system often concurrent with gastrulation
# Neural Plate - thicker region of ectoderm forms above notochord # Neural Folds & Groove - neural ectoderm forms lateral ridges or folds & a deep pit between folds # Neural Tube - folds sink deeper & folds grow together * neurocoel or neural cavity remains inside tube later enlarges to form brain's ventricles # Brain Formation * tube grows fastest at its anterior end * brain first expands into 3 enlarged regions & later 5 |
|
C. Atypical Neurulation
|
* Events
o solid keel of ectoderm sinks deep o then neurocoel cavity forms * Taxa o lamprey - Cephalaspidomorphi o teleosts - highly derived members of the Actinopterygii |
|
Induction of Vertebrae: Normal and abnormal
|
Normal Event
* presence of neural tube stimulates vertebral formation * ensures that both of these structures grow as a functional unit Abnormalities - Anencephaly & Spina Bifida * abnormal conditions where neural tube fails to close * 10% of U.S. population suffers some form of spina bifida * risk decreases when women take 400 mg folic acid daily (before pregnancy begins) * Variation o location along spinal cord or brain differs & severity differs o errors in skin, meninges around spinal cord or vertebral formation o most severe are cases with incompletely closed tube; neurons can't develop |
|
Neural Crest (ectomesenchyme) Cells: What clades have them, location, function?
|
* derived trait in vertebrates
* cells that pinch off of neural tube mass early & migrate to # locations in body * Some Derivatives - branchial skeleton; chromatophores; dentine; # nerve ganglia - sympathetic, parasympathetic, dorsal root (sensory); Schwann cells |
|
Epidermal Placodes
|
* derived trait in vertebrates
* special regions of ectoderm sink beneath surface of skin * Some Derivatives - lens of eye; otic capsule; lateral line organs; contributes to some cranial ganglia |
|
Prototheria Development
|
* Taxa - monotremes - duck-billed platypus & echidna (spiny anteater)
* Typical Amniote Pattern o Macrolecithal Egg o Telolecithal Egg & Discoidal Cleavage o Blastodisc forms on top of yolk o Primitive Streak & Hensen's node - Gastrulation |
|
Theria Development
|
* Taxa - marsupials & placental mammals
* Derived Features o Microlecithal Egg - secondarily derived o Isolecithal Yolk Distribution & Equal Cleavage - secondarily derived o Secondarily derived means trait was present in an ancestor [primary derivation], then lost & finally reappears in modified form for second time in a descendant |
|
Eutheria Development
|
* Blastocyst - new design for "blastula" stage
o Trophoblast [troph = eat] + assume it's not homologous to a "trophoblast" layer found in marsupials - development & location differ + cells form on outer sphere of cells around future embryo + form the earliest attachment of embryo to uterine wall + digest uterine tissues for nutrients to feed developing embryo before placenta forms + contribute to formation of placenta o Inner Cell Mass - forms the embryo |