"Hows it going" - Neuro 2202.docx

"Hows it going" - Neuro 2202.docx - Ch 1 Why is...

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Ch. 1 Why is cellular differentiation required for metazoans? Cellular differentiation (i.e. cells become progressively different from one another) is required in order to establish a body plan which maximizes chances of survival and reproduction. Describe and contrast preformatism and epigenesis. P: All structures of an individual are present in microscopic form at conception, so development consists of simple growth of structures already present. Thought there was a tiny human inside of the head of a sperm that used the womb like a bun uses an oven to “grow”. E: As the body develops, more complex body structures will begin to appear. This happens because the embryo becomes more complex as it develops, disputing the idea of preformatism. What is the modern understanding of how cells within a metazoan came to be different from one another? More modern definition of cell differentiation: the process by which cells selectively express particular genes and thereby take on a particular structure and perform a particular function within the individual. Modern understanding on how cells came to be different: cells differ in the mix of transcription factors present to interact with the regulatory regions of various genes. Example: the frog’s skin cell contained transcription factors that resulted in the expression of only those genes needed by a skin cell. But when the nucleus was inserted into an egg, a different composition of transcription factors, those in the cytoplasm of the egg, altered gene expression, so that the embryo, and eventually tadpole, was produced. This shows that the eggs cytoplasm contained transcription factors needed to trigger the unfolding pattern of gene expression that would result in cell division to form an embryo. Describe how cellular differentiation is controlled by C. elegans, and explain why no duplicate cells form. The cells in C.elegans form by mosaic specification of cell fate; each cell has its own predetermined fate depending on the amount of transcription factors present in the cytoplasm of the cells after each division. The cytoplasm is not a homogeneous mixture, it has varying concentrations of different transcription factors throughout it. These lead to each cell having its own unique mixture which then gives rise to two other unique cells dividing until every cell needed is made. (ex. Zygote becomes AB and P1, AB becomes ABa and ABp while P1 becomes P2 and EMS, etc) What are the three germ layers, and how do they come about? 1. Ectoderm: the outermost 2. Endoderm: the innermost 3. Mesoderm: the middle germ layer. They come about by the formation of the gastrula changing the blastula into an embryo with three obvious layers. What are the three major contributions of ectoderm, and which two parts will make up the nervous system?
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