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B5 Growth and development

Activity AB5.14 Looking at DNA microarrays

To study Remember that particular cells make use of particular genes. Not all genes in a nucleus are active. Scientists can find out which genes are active in a particular tissue by using microarrays. A microarray is a bit like a square glass cover slip marked with thousands of tiny squares. On every square, a robot sticks down one piece of DNA. Each piece of DNA is a different gene. So there can be thousands of genes on one microarray. The DNA on the microarray has one strand instead of two. So another single strand of DNA with the right sequence of bases can stick to it. When scientists want to test a tissue for active genes, they: • extract mRNA from the tissue (active genes make mRNA)

• make single strands of DNA from the mRNA

• label the DNA strands with fluorescent dye

• cover the microarray with the marked DNA then wash off any that didn’t stick

The glowing squares show which genes are active.

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© University of York (UYSEG) and the Nuffield Foundation • This page may be copied solely for use in the purchaser’s school or college

B5 Growth and development

Activity AB5.14 Looking at DNA microarrays Scientists use microarrays to: • find new genes

• test new drugs

• diagnose disease

• look at human variation

To answer 1 Explain why a strand of DNA will bind to another DNA strand only if the two strands have the correct sequence. ……………………………………………………………………... 2 a Complete this diagram to show the order of bases on the single stranded DNA. (Remember that U on mRNA pairs with A on DNA.)

b Colour the dye molecule. c On this microarray DNA, fill in the bases that will bind to the single stranded DNA above.

d How many active genes does the microarray in the diagram show? …………………………………………………………….. e Explain why a microarray can only show which genes are active, not which genes are present in the cell. …………………………………………………………….. …………………………………………………………….. © University of York (UYSEG) and the Nuffield Foundation • This page may be copied solely for use in the purchaser’s school or college

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B5 Growth and development

Activity AB5.14 Looking at DNA microarrays 3 Scientists wanted to know which genes were active in breast cancer cells but not in healthy breast cells. This is a simplified set of results. These genes were active in the healthy breast tissue: A2 B6 C1 D1 E3 F2

A5 C3 D2 E5 F4

C4 D4

C5 D5

These genes were active in breast cancer tissue: A2 B6 C1 D1 E5 F2

A5 C3 D2

C4 D4

D5

F4

a Draw coloured dots into the microarray table above as follows: • red dots for genes present in cancer tissue only • green dots for genes present in healthy tissue only • yellow dots for genes present in both cancer and healthy tissue b Suggest which genes could be studied further to see if their presence or absence stimulates the development of cancer. …………………………………………………………………. …………………………………………………………………. …………………………………………………………………. B5-60

© University of York (UYSEG) and the Nuffield Foundation • This page may be copied solely for use in the purchaser’s school or college

B5 Growth and development

Activity AB5.14 Looking at DNA microarrays Optional 4 Study the microarray analysis below. The results from two tissue analyses were combined to form this pattern – muscle tissue and adrenal gland tissue. Adrenal glands secrete the hormone adrenalin.

Combined microarray analysis results for muscle and adrenal gland tissue

a Use the microarray above to match up these genes with their correct description: C6 A6 F3 D2 • genes for enzymes involved in cell respiration ………………… • gene coding for a protein involved in muscle contraction ………………… • gene coding for synthesis of adrenalin ………………… b Explain why there are some squares where no DNA binds. ………………………………………………………………… ………………………………………………………………… ………………………………………………………………… …………………………………………………………………

© University of York (UYSEG) and the Nuffield Foundation • This page may be copied solely for use in the purchaser’s school or college

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