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Development - I Development a Stages of development(Humans...

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I. Development a. Stages of development (Humans) i. Cleavage ii. Blastulation iii. Gastrulation iv. Organogenesis 1. neurulation 2. other systems b. control of development i. What controls? gene expression 1. cytoplasmic substances 2. induction ii. evidence/ cloning Differing life history – Traits / strategies 4 typical organisms use for research of development each with different amounts of yolk in egg o Echniderms – starfish eggs are tiny with virtually no yolk o Frog egg has moderate amount of yolk lasting until develops to tadpole o Chickens egg has lots of yolk meaning lots of food to eat in development o Humans no yolk in egg, buy embryo develops in but embryo develops in uterus & is fed through umbilical cord 2) Fertilization – group of events, not just single event (gamete anatomy) a) human sperm: acrosome – structure at tip of sperm; membrane containing enzyme b) human egg (2 nd oocyte) anatomy: in 2 nd oocyte zona pellucida – non-celllar clear area granulose cells – exterior to zona pellucide; parts of follicle blastomere(?) blastula imples the whole thing develops into the organism; blastocyst is when only a portion of the unit develops into the embryo o twins: identical (monozygotic) 2 inner cell mass begins totipotency – cells giving rise to placenta & any other cell pluripotency – cells can give rise to many but not all parts of organism (can be used for organs, etc); restricted/ limited abilities o conjoined twins: inner cell mass begins to but does not completely divide, resulting in shared reigions of the body o fraternal twins: 2 eggs are fertilized; dizygotic after 10 days: embryo implanted blastulation ending, gastrulatoin beings
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hCG secretion totipotency ends At about 3 days old : morula (p. 973) - about 32 blastomeres - nearing uterus, approaching end of oviduct - Cleavage – rapid cell division; constant mitotic divisions - no cell growth or increase in organism size - blastomeres – undifferentiated, generic new cells formed by mitotic divisions o Benefits: -smaller pieces build up to larger unit -better surface area/volume ratio Protostomes: spiral cleavage Deutorestome: radial cleavage o Different cleavage patterns determined by amount/presence of yolk - cytokinesis is harder to perform with lots of yolk present holoblastic cleavage - entire volume of zygote is continually divided equal holoblastic – equal-sized blastomeres result from the constant division -i.e. starfish; organisms with little yolk -microlecithal cells – little yolk; equal holoblsatic -isolecithal – even distribution of yolk unequal holoblastic – mesolecithal (moderate amount of yolk) -i.e. frog: divisions tend to favor one end resulting in more blastomeres at the end with the yolk Animal pole: Vegetal pole: meroblastic cleavage -only part of original volume is continuously divided -macrolecithal – lots of yolk -telolecithal – yolk favors one side i.e. birds, reptiles 3) blastulation - change in structure but not in size (change in internal organization) -
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