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Lecture 23 - Lecture 23 11:36:00 AM The process of...

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Lecture 23 31/10/2007 11:36:00 The process of development Progressive changes in shape, form, and function that occur during an  organism’s life cycle Multicellular organisms develop through a series of embryonic stages and  eventually into an adult Typical example of vertebrate development (frog) o Egg and sperm join to form a zygote o Rapid cell division occurs (1 cell to trillions in a matter of days) o Poles and sub-cellular regions are established Gastrulation o Nervous system development o Vestigial organs (tails, arms, toes, etc…) are shed o Development of pertinent structures and organs o Development of germ cells for further propagation Development involves significant change over space and time Use frogs to study because they develop quickly and have transparent  embryos o Can see everything unlike a developing chicken (inside an egg) or a  human or a mammal (in uterus) Development is continuous throughout life until death o Studies in development is useful to study aging and life span  expansion o Body is made up of 100 trillion cells Made up of >200 different cell types Cells can be specialized 
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Muscle cells Neurons Immune cells Allows an entire body to function Problem is that with so many cells and cell types if things  go wrong, the results can be fairly detrimental o When some cells divide, they are charged with different developmental  programs Utilize different genes at different levels to develop the structure  and frame work for organism organization Ectoderm (outer layer) Skin cells and nervous system Mesoderm (middle layer) Blood cells, muscle cells, kidneys Endoderm (inside layer) Digestive tract and lungs Germline Sex cells (sperm and egg) Development occurs in all organisms Bacteria o In response to environmental stimulation a bacteria can alter its  developmental program Instead of dividing in half to make 2 equal cells, a bacteria can  divide asymmetrically An inner cell generates (spore) An out cell develops (mother cell)
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