General uniformity in fate of cells for spiral, determinate development: ectoderm from first quartet of cells entoderm from 4a, 4b, 4c, and 4Q cells mesoderm from 4d cell Indeterminate development - cell fate is determined later in development. Embryo will not develop properly if cells are removed. indeterminate developmentĭeterminate development - fates of early blastomeres (2-4 cell stage) fixed. Allows embryologists to follow cell fates and compare development in various taxa.Ĩ Determinate vs.
Macromeres and micromeres are grouped into quartets and numbered according to first quartet ancestor and number of cell divisions. Wilson developed a numbering scheme to follow individual cells through spiral cleavage.
Top cells are micromeres and bottom cells are macromeres.ħ Spiral cleavage E.B. Radial cleavage Spiral cleavage First quartet of cells Second quartet lies directly on top of first quartet Second quartet lies in depressions between first quartet. 003_04caddis3.jpgĥ Cell cleavage First cell division is parallel to the animal-vegetal pole (longitudinal division) Second cell division is also parallel to the animal-vegetal pole Third cell division is perpendicular to the animal-vegetal pole (transverse division), sometimes resulting in micromeres and macromeres Meroblastic cleavage - cleavage planes do not pass through dense yolk so blastomeres are not separated from each other. Occurs in isolecithal and weakly telolecithal zygotes. Holoblastic cleavage - cleavage planes pass all the way through the cell. The zygote splits and the resulting cells are blastomeres.
indirect development 001_04caddis1.jpgĢ Types of Eggs Animal pole - tends to become other regions of the embryo 002_04caddis2.jpg Vegetal pole - tends to become digestive systemģ Types of Eggs Isolecithal - scanty yolk distributed uniformly through egg Centrolecithal - yolk distributed in center around nucleus Telolecithal - yolk concentrated at vegetal pole 002_04caddis2.jpgĤ Cell cleavage A fertilized egg is a zygote. indeterminate development Blastulae Gastrulation Mesoderm formation Coelom formation Direct vs. spiral"- Presentation transcript:ġ Development Types of eggs Cell cleavage radial vs. Presentation on theme: "Development Types of eggs Cell cleavage radial vs.
0 kommentar(er)
