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	Cleavage and Blastulation
		Cleavage is the process after fertilization when early mitotic cell divisions occur that progressively reduce cell size.
		The symmetry of cleavage is further divided into subtypes such as radial or spiral, depending on the position of the yolk.
		Spiral cleavage is yet another symmetry of cell divisions that occurs in mollusks and roundworms.
	main.uab.edu /show.asp?durki=19952 (1252 words)

	Cleavage (embryo) - Wikipedia, the free encyclopedia
		In embryology, cleavage is the division of cells in the early embryo.
		Radial cleavage is characteristic of the deuterostomes, which inlude some vertebrates and echinoderms, in which the spindle axes are parallel or at right angles to the polar axis of the oocyte.
		In spiral cleavage, the cleavage planes are oriented obliquely to the polar axis of the oocyte.
	en.wikipedia.org /wiki/Cleavage_(embryo) (602 words)

	Modified spiral cleavage: the duet cleavage pattern and early blastomere fates in the acoel turbellarian Neochildia ... (Site not responding. Last check: 2007-11-06)
		Modified spiral cleavage: the duet cleavage pattern and early blastomere fates in the acoel turbellarian Neochildia fusca.
		Author: Martindale, Mark Q. The acoel turbellarian Neochildia fusca exhibits modified spiral cleavage which is characterized by the formation of pairs of micromeres (duets) from the vegetal macromeres after the two-cell stage.
		Spiral cleavage, which characterizes the embryos of phyla belonging to the Spiralia, typically involves the generation of four quartets of micromeres from the four macromeres produced by the first and second...
	www.highbeam.com /library/doc0.asp?DOCID=1G1:18965744&refid=ip_encyclopedia_hf (182 words)

	DEVELOPMENTAL BIOLOGY: ON MORPHOGENS
		Spiral cleavage is characterized by the oblique angle of the early cleavage planes and the alternation of direction of successive divisions.
		In this view, spiral cleavage is controlled by an asymmetry in the cortex that regulates the inclination of the mitotic apparatus prior to cytokinesis.
		By contrast, Meshcheryakov and Beloussov (5) attributed the reversal of cleavage pattern between sinistral and dextral species to a reversal -- from clockwise to anti-clockwise -- of the spiral rotation of the daughter micromeres during cytokinesis.
	scienceweek.com /2006/sw060203-6.htm (1694 words)

	Evolutionary modifications of the spiralian developmental program American Zoologist - Find Articles
		This paper examines the evolution of development in the Spiralia, including the cleavage pattern, cell lineage, and mechanisms of blastomere specification and dorsoventral axis determination, with particular emphasis on the polyclad turbellarians which are assumed to be the extant basally-branching members of the group.
		With the completion of the second cleavage division the four principal embryonic cell quadrants are established, which subsequently give rise to quartets of smaller animal pole micromeres, identified by a lower case letter corresponding to that of the mother cell and a number preceding the letter indicating the quartet to which they belong.
		Most often third cleavage is in a dexiotropic or clockwise direction, followed by alternating laeotropic and dexiotropic divisions, so that the arrangement of cells gives a spiral appearance when viewed from the animal pole.
	www.findarticles.com /p/articles/mi_qa3746/is_199809/ai_n8815290 (731 words)

	[No title] (Site not responding. Last check: 2007-11-06)
		The animal cells are displaced in a spiral arrangement.
		Handedness is maternally specified and dextral spiral is genetically dominant to sinistral.
		The body axes are defined by early cleavages and cytoplasmic determinants are clearly important.
	www.oup.co.uk /powerpoint/bt/wolpert2/ch06.ppt (1969 words)

	Teaching Animal Molecular Phylogenetics (Site not responding. Last check: 2007-11-06)
		Since Annelida, Mollusca, and some other coelomate protostomes have spiral cleavage, many authors assume that all protostomates have spiral cleavage as the plesiomorphic condition, even arthropods and other groups where the actual cleavage pattern is usually not spiral.
		Other authors, however, restrict the term "Spiralia" to phyla in which spiral cleavage is actually and unequivocally observed, though not necessarily in all species.
		Spiral cleavage is not seen in Nematoda or in Arthropoda except for a few crustaceans.
	www.mhhe.com /biosci/pae/zoology/animalphylogenetics/section03.mhtml (6091 words)

	Cleavage - True Meaning of Cleavage, The - Reviews, Best Prices and Product (Site not responding. Last check: 2007-11-06)
		In some embryos, the daughter blastomeres are either above or to the This latter cleavage symmetry is said to be spiral.
		Cleavage of BID by caspase 8 mediates the mitochondrial damage in the Fas pathway of apoptosis.
		Cleavage in general refers to a division or separation of form.
	linksseek.com /lksk/cleavage.html (424 words)

	[No title]
		In spiral cleavage the first two divisions of the egg are equal, but the rest are unequal.
		Cleavage is determinate - This means that the fate of each individual cell is already established when it is formed.
		Cleavage is indeterminate.This means that the fate of each individual cell is not determined when it is formed and each cell can form one of many cell types.
	www.gwu.edu /~darwin/BiSc151/Coelom/Coelom.html (543 words)

	Cleavage patterns and gastrulation as complex characters for phylogenetic inferences in the Metazoa: a contribution to ... (Site not responding. Last check: 2007-11-06)
		Cleavage patterns and gastrulation as complex characters for phylogenetic inferences in the Metazoa: a contribution to the Articulata/Ecdysozoa controversy
		The Articulata hypothesis implies a derivation of the arthropod cleavage from the spiral cleavage mode.
		To fill these gaps we want to study the early cleavage patterns, the cell lineages, the cell fates, and the gastrulation modes of representatives of the Pantopoda (Chelicerata) and the Cirripedia (Crustacea) in great detail with a variety of methods ranging from histology to 4-D microscopy.
	www.hu-berlin.de /forschung/fdb/english/PJ/PJ7151.html (245 words)

	EMBRYOGENY AND LARVAL DEVELOPMENT (Site not responding. Last check: 2007-11-06)
		The orientation of the blastomeres can also be described directionally by radial cleavage or spiral cleavage, refering to how the subsequent divisions took place.
		In indeterminate cleavage, the cells ìfateî is not fixed until after the 4-cell, or possible later, stage.
		In general, the ìolderî groups of invertebrates (protostomes) exhibit spiral, determinate cleavage, while the ìyoungerî groups (deuterostomes) exhibit radial, indeterminate cleavage, similiar to that of vertebrates.
	bioweb.wku.edu /courses/biol225/225urchins.html (584 words)

	Pharyngula: Spiral cleavage
		A quartet of micromeres is displaced anticlockwise in the levotropic cleavage (blue arrow, left) and clockwise in the dextrotropic cleavage (blue arrow, right) when viewed from the animal pole.
		Arrowheads in (B) indicate the direction of the spiral deformation (SD) of the dextral embryos.
		The mutation in the sinistral form destroys the precise spiral asymmetry of the early embryo, but one unexplained phenomenon is that after the third division, the micromeres still migrate towards the furrows between the macromeres…but they consistently twist to the left instead of the right.
	scienceblogs.com /pharyngula/2006/04/spiral_cleavage.php (2250 words)

	Classification of the Lophophorates Based on Hox genes and 18S rDNA Analyses: A Comparison to the Traditional ... (Site not responding. Last check: 2007-11-06)
		Based on cleavage patterns, lophophorates appear to be deuterostomes because radial cleavage is a characteristic of deuterostomes (Meglitsch and Schram, 1991).
		Valentine (1997) and de Rosa (2001) suggest that radial cleavage patterns are ancestral to spiral cleavage patterns, based on the principle of parsimony.
		De Rosa (2001) feels that cleavage pattern is not a reliable character for phylogeny because of the great variability and shifts between the two cleavage types seen in cephalopods, nematodes, acoel flatworms, and many vertebrate and arthropod taxa.
	www.susqu.edu /students/b/bowlinge/LophophoratePaper.htm (2833 words)

	16anim5
		Cleavage begins with the first mitotic division of the zygote and ends when a hollow sphere of cells, the blastula, is produced.
		Another developmental difference between the protostomes and the deuterostomes is the pattern of cell cytokinesis that occurs during cleavage.
		In the protostomes, after the 4 cell stage, the embryo exhibits spiral cleavage.
	io.uwinnipeg.ca /~simmons/16cm05/1116/16anim5.htm (2059 words)

	Pharyngula
		That is, most molluscs divide in a very specific way, with a pattern that results at the third cleavage in a set of four small cells (micromeres) stacked on top of four large cells (macromeres) with a slight clockwise or counterclockwise twist (the direction of the twist is genetically controlled).
		Cephalopods have abandoned the molluscan stereotype of spiral cleavage, mosaicism, trochophore feeding stage, and minimal parental investment in their offspring altogether, and instead produce large yolky eggs.
		They have also converged on a solution just like that of birds—early cleavages are only partial, and they form a patch of dividing cells in one spot on the yolk, and build a bird-like blastodisc.
	pharyngula.org /index/weblog/print/256 (644 words)

	Re: What are the 'advantages' of developing a deuterostome pattern of embryonic
		The main feature of Deuterostomes that they have used to their advantages is radial cleavage, or more correctly, no spiral cleavage.
		The mechanism of spiral cleavage involves realigning the mitotic spindles 90° after each division.
		Another advantage/disadvantage to randomizing cleavage is the inability to use the cleavage pattern as a foundation for the body plan.
	www.madsci.org /posts/archives/feb99/918160589.Dv.r.html (799 words)

	Cleavage patterns and the topology of the metazoan tree of life -- Valentine 94 (15): 8001 -- Proceedings of the ...
		Cleavage patterns and the topology of the metazoan tree of life
		The phyla of the lophotrochozoan alliance are divided between radial and spiral cleavages.
		on the evolution of cleavage and its consequences.
	www.pnas.org /cgi/content/full/94/15/8001 (4052 words)

	Lecture 15: Development, Coelom Formation
		Cleavage is telolecithal eggs is meroblastic – cleavage furrows extend only part way through the egg
		Radial cleavage – cleavage furrows are oriented parallel or perpendicular to animal-vegetal pole axis
		Spiral cleavage – cleavage furrows are oriented obliquely to animal vegetal pole – blastomeres end up lying in cleavage furrows
	www.humboldt.edu /~zool110/Lectures/Lecture15.htm (822 words)

	Biology 104 Spring 2004
		Sea urchins and amphibian eggs have radial cleavage; for example in the third cleavage (4 cells-> 8 cells), the 4 cells near the animal pole are each directly over one of the 4 vegetal cells.
		In spiral cleavage, the geometric arrangement is more like stacking cannon balls or oranges, in that the 4 top cells are centered over the boundaries between the 4 bottom cells.
		Polar lobes are large bumps that form on the surface of one of the cleaving cells, in some species during the first cleavage division, in other species during both of the first TWO cleave divisions and in a few species polar lobes form during all three of the first three cleavages.
	www.bio.unc.edu /faculty/harris/Courses/2004biol104/lecture13.html (1706 words)

	Modified spiral cleavage: the duet cleavage pattern and early blastomere fates in the acoel turbellarian Neochildia ... (Site not responding. Last check: 2007-11-06)
		Spiral cleavage, which characterizes the embryos of phyla belonging to the Spiralia, typically involves the generation of four quartets of micromeres from the four macromeres produced by the first and second cleavages.
		The direction of the cleavage planes forming the micromere quartets alternates between dexiotropic (clockwise) and laeotropic (counterclockwise), with the first quartet usually resulting from a dexiotropic division to the eight-cell stage.
		Cell lineage studies of embryos with quartet spiral cleavage demonstrate that the first three quartets form ectoderm (1).
	calbears.findarticles.com /p/articles/mi_hb1456/is_199610/ai_n6376123 (263 words)

	Rachel Zindren
		The difference between spiral and radial cleavage is the direction in which the cells divide.
		During spiral cleavage, cells divide diagonally, whereas during radial cleavage cells divide perpendicular or parallel to the embryo
		In determinate cleavage the fate of the cells in decided early on, whereas in indeterminate cleavage the cells continue to have the ability to become many different types of cells
	www.personal.psu.edu /users/r/l/rlz124/sharedfeatures.htm (405 words)

	Glossary
		In animals where cleavage (cell division) involves the whole egg, the blastula usually consists of a hollow ball of cells.
		Reductive divisions are characteristic of cleavage in early embryos.
		spiral cleavage-Pattern of early cleavage found in molluscs and annelids (both mosaic eggs).
	worms.zoology.wisc.edu /frogs/glossary.html (3741 words)

	[No title]
		Spiral cleavage- planes of cell division are diagonal to the vertical axis of the embryo.
		Radial cleavage- planes are either parallel or perpendicular to the vertical axis of the egg; as seen in the eight-cell stage, the tiers of cells are aligned, one directly above the other.
		Determinate cleavage- protostomes rigidly casts the developmental fate of each embryonic cell very early Indeterminate cleavage- each cell produced by early cleavage divisions retains the capacity to develop into a complete embryo.
	www.angelfire.com /ca/finkar/bio1202ch32.doc (1294 words)

	Biology 205 Course Glossary Q-Z (Site not responding. Last check: 2007-11-06)
		a type of cleavage pattern found in deuterostomes (echinoderms, chordates) in which the daughter cells cleave off without rotation.
		Contrast with spiral cleavage of protostomes (annelids, molluscs, arthropods)
		Spiral cleavage is found in the group of animals known as protostomes: annelids, arthropods, molluscs
	www.botany.ubc.ca /bleander/biol205/Glos4.html (2186 words)

	Review of "Homology, An Unsolved Problem" - TheologyWeb Campus
		A survey of the literature indicates that that conventional biology identifies spiral cleavage with protostomes, and radial cleavage with deuterostomes.
		The “problem” of spiral cleavage being incompletely characteristic of protostomes seems to be pretty much resolved.
		This is strong circumstantial evidence that the common ancestor had spiral cleavage, and that loss of this feature is a secondary characteristic in some lineages.
	www.theologyweb.com /campus/showthread.php?t=46837 (9003 words)

	Mark Martindale - Department of Zoology, University of Hawaii
		Is there evidence for the origins of major cleavage patterns in bilaterian development (e.g., spiral and radial cleavage) in radially symmetrical forms?
		The third area of interest is to understand the role of the early cleavage program in the segregation of developmental potential in a wide variety of animals which share a mode of embryogenesis known as spiral cleavage (e.g.
		We are also interested in understanding the significance of naturally evolved variations in the spiral cleavage program such as modifications associated with the abandonment of larval development in order to develop directly to a miniature adult form (direct development).
	www.hawaii.edu /zoology/faculty/martindale.htm (697 words)

	Dr. Mark Q. Martindale, Kewalo Marine Laboratory
		The first area of interest is to understand the role of the early cleavage program in the segregation of developmental potentialin a wide variety of animals which share a mode of embryogenesis known as spiral cleavage (e.g.
		We are also interested in understanding the origins and significance of naturally evolved variations in the spiral cleavage program such as modifications associated with the abandonment of larval development in order to develop directly to a miniature adult form (direct development).
		The use of intracellular cell lineage labeling and cell ablation techniques in a wide variety of species are consistently used for experiments.
	www.kewalo.hawaii.edu /labs/martindale (1263 words)

	Embryogenesis and Development of Epimenia babai (Mollusca Neomeniomorpha) -- Okusu 203 (1): 87 -- The Biological ...
		cleavage stage and one at the second cleavage stage.
		by alternation of chirality: the fourth cleavage was sinistral
		and the fifth cleavage was dextral, producing 32 cells (Fig.
	www.biolbull.org /cgi/content/full/203/1/87 (5335 words)

	Special Feature: Evolution of the bilaterian body plan: What have we learned from annelids? -- Shankland and Seaver 97 ...
		Annelids undergo a mode of embryonic development known as spiral cleavage (Fig.
		Beginning with the third round of cleavage, the A, B, C, and D blastomeres cleave off (arrows) quartets of smaller cells called micromeres at the animal pole.
		In spiral cleavage, each quartet of micromeres is rotated with respect to the parent blastomere, and the chirality of rotation alternates for odd- and even-numbered quartets.
	www.pnas.org /cgi/content/full/97/9/4434 (3380 words)

	Cleavage: Radial vs. Spiral (Site not responding. Last check: 2007-11-06)
		One of the hallmarks of deuterstome development is that early cleavage divisions are radial.
		Play the movie at the below right to get a sense for the difference between these two cleavage patterens in two generalized embryos.
		Differences in cleavage orientation in idealized spirally and radially cleaving embryos
	worms.zoology.wisc.edu /frogs/cleavage/clea_radspir.html (70 words)

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