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Genes & Development Packet #49 Chapter #21
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Development
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Introduction Development
The process by which descendents of a single cell specialize and organize into a complex organism Development is accomplished via the use of stem cells.
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Stem Cells Stem cells Have the ability to produce differentiated descendents, yet retain the ability to divide to maintain the stem cell population. There are two categories of stem cells.
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Stem Cells II Stem cells Totipotent stem cells Pluriopotent stem cells
Give rise to all cell types Pluriopotent stem cells Give rise to many, but not all, types of cells in an organism Not capable of forming a functional organism.
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Stem Cells III Stem cells Totipotent
Give rise to all types of stem cells Pluriopotent Gives rise to many, but not all, types of cells.
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How do Cells Develop?
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Introduction I During the development of cells, cells must go through two phases. Commitment Cell Differentiation Stem Cells Commitment Specification Determination Cell Differentiation
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Introduction II Commitment Cell Differentiation
The official series of overt changes in cellular biochemistry, and function. The cell commits to a certain fate. Two stages Specification When cell is capable of differentiating autonomously (independent of the surroundings) when placed in a neutral environment (Petri dish or test tube) Determination When cell is capable of differentiating when placed into autonomously when placed into another region of the embryo. Cell Differentiation The development of specialized cell types
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Differential Gene Expression
The cause of differences among various cell types. Has three postulates Every cell nucleus contains the complete genome established in the fertilized egg Unused genes in differentiated cells are not destroyed or mutated, and they retain the potential for being expressed Only a small percentage of the genome is expressed in each cell Hence a small portion of RNA is synthesized specified for that cell type
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Other Important Terms Nuclear Equivalence Totipotency
All nuclei, with a few exceptions, of differentiated somatic cells of an organism are identical to each other and to the nucleus of the single cell from which they descended. Genomic rearrangement Gene amplification Totipotency Capability of cells to direct the development of an entire organism
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Categories of Genes
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Genes & Development of Cells
Maternal Effect Genes Segmentation Genes Homeotic Genes
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Maternal Genes
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Maternal Effect Genes I
Genes expressed in the mother’s ovaries that produce mRNA’s that are ultimately placed in different regions of the developing egg Establish the polarity of in the embryo. Axis specification Anterior vs. Posterior ends
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Maternal Effect Genes II
The proteins produced from the mRNA transcribed from the maternal effect genes are types of morphogens. Bicod & Hunchback proteins Regulate the production of anterior structures of the embryos. Nanos & Caudal proteins Regulates the formation of the posterior structures of the embryos. These proteins may behave as transcription factors that turn on HOX genes ultimately leading to the separation of the anterior from the posterior end Morphogen A soluble substance, chemical agent, that affects differentiation and specification of any totipotent cell.
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Maternal Effect Genes III
Maternal Genes Bicod & Hunchback proteins Anterior regions Nanos & Caudal proteins Posterior regions
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Segmentation Genes
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Segmentation Genes The proteins produced, as a result of the transcription of the Maternal Effect Genes, affect a class of genes called the segmentation genes. Genes responsible for the transition from cell specification to cell determination. In drosophila, divide the early embryo into a repeating series of segmental primordia along the anterior-posterior axis. Divide the embryo into 14 parasegments.
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Classes of Segmentation Genes
Gap Genes Organization of regions Pair Rule Genes Divides segments into parasegments Segment Polarity Genes Maintains repeated structures within each segment Gap Genes Pair Rule Genes Segment Polarity Genes
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Classes of Segmentation Genes
Gap Genes Respond to the concentrations of the material effect gene proteins The first set of segmentation genes to act Gap gene proteins define specific regions of the embryo Begin organization of the body into anterior, middle and posterior regions Gap gene proteins activate and repress the pair-rule genes
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Classes of Segmentation Genes II
Pair Rule Genes Proteins of pair-rule genes subdivide the broad gap gene regions, mentioned previously, into parasegments Segment Polarity Genes Responsible for maintaining certain repeated structures within each segment Allowing for cell fates to be firmly established.
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Homeotic Genes
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Homeotic Genes--Fruit Flies
Regulated by gap, and pair rule, genes. Responsible for specifying the “identity” of each segment Wings Legs
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Review
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Homework Assignment What are the impacts of mutations in the Gap genes, pair rule genes and the homeotic genes.
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Cloning Nuclear Transplantation Dolly The Sheep
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