| Property | Mammal | Sea Urchin |
|---|---|---|
| Oocyte size | 1/10 millimeter | ~ same |
| Polar body size | quite large, visible | tiny, not visible |
| Yolk concentration | moderate | same |
| Stage of meiosis at fertilization | diploid | haploid |
| Fast block to polyspermy | like nerve action potential (electric depolarization) |
same |
| Slow block to polyspermy | secretion of cortical granules | also |
| enzymes digest adhesion proteins | also | |
| fertilization "membrane" | ||
| Cleavage divisions | Not synchronous | synchronous |
| "Holoblastic" | same | |
| ~ 15-20 hour cell cycle | fast (half hour cell cycle) |
|
| forms blastocyst | forms blastula | |
| Body develops from | only the inner cell mass | the whole blastula |
| Gastrulation | cell ingression | ingression of "primary mesenchyme" |
| then invagination at vegetal pole and also secondary mesenchyme |
||
| ~ 95% placenta, ~ 5% body | entire gastrula becomes body larva |
| animal | oocytes | cleavage | gastrulation |
|---|---|---|---|
| Amphibian | diploid | holoblastic (barely) | blastopore |
| Bird & Reptile | diploid | meroblastic | primitive streak |
| Mammal | diploid in most tetraploid in dog |
holoblastic | primitive streak |
| Teleost fish | diploid | meroblastic | epiboly |