DNA microarrays

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Each spot contains a picomole of a DNA (10-12 moles) sequence

• With only a few exceptions, every cell of the body

contains a full set of chromosomes and

identical genes. Only a fraction of these genes are

turned on, however, and it is the subset that is "expressed" that confers unique properties to each

cell type.

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• "Gene expression" is the term used to describe the transcription of the information contained within the DNA, into messenger RNA (mRNA). Molecules are then translated into the proteins that perform most of the critical functions of cells.

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•We study the mRNA produced

by a cell to learn which genes are expressed

…

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•Microarrays allow scientists to analyze expression (the turning on of genes)of many genes in a single experiment quickly and efficiently.

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•This technology allows us to analyze the roles that specific

genes play in disease.

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• researchers have identified a large number of genes

within sequences.

• Since we know where they are… we can see if they

are turned on

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• A microarray works by exploiting the ability of an mRNA molecule to bind specifically to, or

hybridize to, the DNA template from which it originated.

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DNA

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each spot on an array is associated with a particular gene. Many genes

are arranged in a regular pattern

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We can survey MANY genes, from one cell QUICKLY and at the same

time

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Now, consider two cells: cell type 1, a healthy cell, and cell type 2, a diseased cell. Both

contain an identical set of four genes, A, B, C, and D. Scientists are interested in determining

the expression profile of these four genes in the two cell types.

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Note: this is a merged image from both individual cells…

Now compare…

• Green = control cell “healthy”

• Red = diseased cell

• Yellow = simultaneous Yellow = simultaneous expression (which expression (which genes show up in both)genes show up in both)

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you may conclude that both cell types express gene A at the same level, that cell

1 expresses more of gene B, that cell 2 expresses more of gene C, and that

neither cell expresses gene D.

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• Green = control cell• Red = diseased cell

• Yellow = simultaneous Yellow = simultaneous expressionexpression

• Black = no expressionBlack = no expression

The color, & its intensity tells if the normal gene or the mutation is present in the

control cell or the diseased cell

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• Green = control cell• Red = diseased cell

• Yellow = simultaneous Yellow = simultaneous expressionexpression

• Black = no expressionBlack = no expression

• microarray-based gene expression profiling can be used to identify genes whose expression is changed in response to pathogens or other organisms by comparing gene expression in infected to that in uninfected cells or tissues.