Unit 7 Notes

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Biological Sciences
Diane O' Dowd

Differential Gene Expression  Different Cell Types in a Multicellular Organism A Genetic Program for Embryonic Development  Zygote  organism: o Cell division, cell differentiation, and morphogenesis  Cells undergo cell differentiation- the process by which cells become specialized in structure and function o Morphogenesis- the physical processes that give an organism its shape  Cells are not randomly distributed but organized into tissues  Activities of a cell depend on the gene it expresses and the proteins it produces  Different fully differentiated cells has a particular mix of specific activators that turn on the collection of genes whose products are required in the cell o Materials placed into the egg by the mother set up a sequential program of gene regulation that is carried out as cells divide  1. How cells that arise from early embryonic mitoses develop the differences that start each cell along its own differentiation pathway  2. How cellular differentiation leads to one particular cell type Cytoplasmic Determinants and Inductive Signals  Two sources of information tell a cell which genes to express at any given time during embryonic development o 1. Egg’s cytoplasm  Contains both RNA and proteins encoded  Cytoplasm of unfertilized egg is not homogenous • Cytoplasmic determinants spread unevenly throughout and influence the course of early development o Environment around a particular cell  Signals impinging on an embryonic cell from other embryonic cells in the vicinity • Induction- when such signals cause changes in the target cells • Interactions between embryonic cells help induce differentiation of the many specialized cell types making up a new organism Sequential Regulation of Gene Expression During Cellular Differentiation  Determination- the events that lead to the observable differentiation of a cell o Once a cell has undergone determination, an embryonic cell is irreversibly committee to its final fate o Outcome of determination, observable cell differentiation, is marked by the expression of genes for tissue-specific proteins  These proteins found only in a specific cell type  Evidence of differentiation: • Appearance of mRNAs for these proteins • Transcription remains the principal regulatory point for maintaining appropriate gene expression • Ex. Muscle cells develop from embryonic precursor cells that have the potential to develop into a number of cell type
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