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Developmental
Lecture 3
| Question | Answer |
|---|---|
| Holoblastic | isolecithal and mesolecithal eggs |
| Radial | Echinoderms and amphibians (mesolecithal - displaced radial) |
| Spiral | Annelids, mulluscs, and flatworms |
| Bilateral | Tunicates |
| Rotational | Mammals and nematodes |
| Cleavage | rapid mitotic division after fertilization |
| Most mammalian species | DNA replication is very intense and therefore no transcription occurs. |
| Process controlled by | maternal effect factors (maternally produced mRNA’s and proteins) |
| During ______ there is an increase in cell number but there is no increase in cell size. Cleavage leads to the formation of a blastula. In a blastula blastomeres surround blastocoel. | cleavage |
| Holoblastic cleavage | Entire cytoplasm of Zygote is partitioned into cells. Seen in species with low to moderate yolk content |
| Meroblastic (incomplete) | telolecithal and centrolecithal eggs |
| Discoidal (telolecithal) | Fish, reptiles and birds |
| Superficial (centrolecithal) | Most insects |
| Meroblastic cleavage | incomplete cleavage |
| This occurs in both ____ and ____ eggs | telolecithal and centrolecithal |
| Radial cleavage | planes are parallel or right angles to the animal – vegetal axis. Produce animals that are radially symmetric i.e., sea urchins or frog. In frog site of sperm entry (180 opposite grey crescent) causes symmetry. |
| Frogs Cleavage - Radial | Blastula is formed at the 128 cell stage with the blastocoel in the animal hemisphere. |
| Sea Urchin Cleavage - Radial | Have a blastula at 128 cell stage |
| No blastocoel is produced | stereoblastula |
| Spiral cleavage occurs in | snails - Cleavage planes are at oblique angles to animal -vegetal axis and produce a spiral arrangement |
| Rotational cleavage occurs in | mammals - 1st Cleavage is Meridional 2nd Cleavage is Meridional in one cell and equatorial in the other |
| Fluid secreted by trophoblast causes blastocoel formation Entire structure is called the | blastocyst |
| The ____ is the mammalian equivalent of a blastula but it is different in that it has the internal cells. | blastocyst |
| Discoidal cleavage occurs in | birds. Birds have telolecithal eggs - Cleavage is restricted to small disc of yolk free cytoplasm (above the yolk) |
| Cleavage produces single layer of cells called | blastoderm |
| Over time cells in center are lost becoming 1 cell layer thick. This is called the ____ ____. Surrounding area (5-6 cells thick) is called the _____ ____ | area pellucida and area opaca |
| New cells produced from the area opaca and pellucida form lower layer called the | hypoblast |
| Upper layer is called the ___ and in between the two layers is the Blastocoel. | epiblast |
| Superficial Cleavage occurs in | Drosophila. Drosophila have centrolecithal eggs. |
| A ____ is a single cell that has multiple nuclei. | Syncytium |
| Cleavage is restricted to nuclei at surface of egg. In Drosophila there are 7 rounds of synchronous mitosis. Cytokinesis does not occur yielding a single cell with many nuclei (syncytium). | ..... |
| Cellularization | is the process by which cell membranes form around the nuclei. |
Created by:
AshCha
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