Similarities and differences between mammal versus sea urchin development

PropertyMammalSea 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)
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


Comparison of amphibians, birds and reptiles, mammals and teleost fish

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



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