Biology 3338A Lecture Notes - Lecture 5: Sea Urchin, Catenin, Notochord
24 Jan 2015
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Document Summary
Cleavage series of mitotic events that divide huge volume of egg cytoplasm into numerous smaller nucleated cells (bastomeres). In most species (mammals are the exception) rates of cell division and placement of balstomeres with respect to each other is under the control of proteins and mrna stored in oocyte. There is no growth in mass (mammals are an exception). Early cleavage patterns are well defined, species specific and indicative of important underlying developmental pathways, and the subsequent inductive interactions. During early development cleavage rhythms are controlled by maternal factors. During early divisions mitotic gap periods (g1 and g2) are abolished. Zygote divides in half, quarters, eighths etc dividing cytoplasm as its goes. Karyokinesis and cytokinesis are distinct, and as such can be regulated separately by the cell. One of the hallmarks of deuterostome development is that early cleavage divisions are radial. Spiral holobalstic cleavage snail (also molluscs, worms)
