Bernal, Griffith Joyner D._BSBio1-4_Lesson2&3_Notes.pdf -...

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Chapter 2. Chordate CharacteristicsChapter 3. Vertebrate StoryChordatesoconsists of 3 groups1.Cephalochordates(amphioxi/lancets)2.Urochordates (tunicates / seasquirts)3.Vertebrates (fishes, amphibians,reptiles, mammals)oshare common fundamental bodyfeatures1.notochord2.pharyngeal slits3.endostyle (thyroid gland)4.dorsal hollow nerve coredformingthe simple central nervous system5.post-anal tailDevelopmental Patterns of Chordates-processofreproductionthroughfertilization (fusion)oEgg and Fertilization-union of sex cells oof the samespeciesdiploid zygotedeveloped zygote form intothemorula,blastulagastrula, and neurula-eggs can be considered as one ofthe largest cell in the bodythese cells are nourished bythe yolkamount of yolk is dependenton the organismusuallyproducedfromvitellogenin-uneven distribution of yolk willallow the polarity of the egg2 poles allow one toidentify the region of theegg yolk and the region ofthe nucleusvegetal pole-area with majority ofthe yolk componentanimal pole-area with the nucleuseggoviparous-lays eggovoviviparous-egg hatches inside theparent’s body-parent produces milk andeggviviparous-noprotectiveshellproduced-developed offspring is bornoCleavage Formation and Blastulation-excessive amounts of yolk will hinderthe proper cleaving of the cell
meroblastic cleavage-cleavage does not fully separatethe cytoplasm of the dividingcellsholoblastic cleavage-cleavage is able to successfullyseparate the cytoplasmradial-in 8-cell stage, the upper layerof cells can be found sittingdirectly on top the lower layerof cellsspiral-in the 8-cell stage, the upperlayer of cells can be foundsitting at the spaces betweenthe cells of the lower layerdiscoidal-a disc is formed during thecleavage formation which isfound on top of the yolkblastula-transformed clump of numerouscells from zygoteblastomere-blastula that each individual ispresent inblastocoel-fluid-filled cavity inside theblastula-during this stage, developing embryohas about a hundred to thousandsof cells each of which containsdifferent cytoplasmic compositionoGastrulation-pertains to the gut formationwherein the endoderm will producethe initial gut of the organism-responsible for the production of thegerm layersectodermendodermmesoderm-positioning of the cells in a gastrulawill give an idea about the eventualinteraction of each region-migration of cells in chordate groupsmay be one of the following:epibolycells spread across theouter surface as a unitinvolutioncells may turninward and then spread over theinternal surfaceinvaginationthe wall of cellswill indent or fold inwarddelaminationsheets of cellsmay split into parallel layersingressionindividual surfacecells may migrate to the interiorof the embryooOrgansprotostomes-mollusks,annelids,andarthropods-where schizocoelus organism orschizocoelomates belong to

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