Q.15 In DNA microarray techniques consist of
(1)large number of ds DNA
(2)large number of ss DNA
(3) small number of ss DNA
(4)large number of ds DNA
DNA microarray techniques consist of a large number of single-stranded DNA (ssDNA) probes. These ssDNA oligonucleotides or cDNAs (typically 25-70 mers) are immobilized in a high-density grid on a solid surface like glass, enabling hybridization with fluorescently labeled target ssDNA or cDNA from samples for gene expression or genotyping analysis.
Option Analysis
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(1) large number of ds DNA: Incorrect—double-stranded DNA cannot hybridize with target sequences; arrays require ssDNA probes for specific Watson-Crick base pairing.
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(2) large number of ss DNA: Correct—microarrays feature thousands to millions of unique ssDNA probes spotted or synthesized in situ (e.g., Affymetrix GeneChips), allowing parallel analysis of entire genomes.
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(3) small number of ss DNA: Wrong—core advantage is high-throughput with >10,000 probes per cm², not low-density formats like Southern blots.
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(4) large number of ds DNA: Duplicate error—dsDNA probes block hybridization sites, making detection impossible without denaturation.
Answer: (2) large number of ss DNA.
Introduction to DNA Microarray Composition
DNA microarray techniques consist of large number of ss DNA probes arrayed on solid supports for high-throughput nucleic acid hybridization. This enables simultaneous analysis of thousands of genes, fundamental to functional genomics and expression profiling.
Why Single-Stranded DNA is Essential
ssDNA probes (cDNA or oligos) specifically hybridize with complementary fluorescent target cDNA via A-T/G-C pairing. dsDNA cannot bind targets, so arrays use denatured or synthesized single strands washed post-hybridization to remove mismatches.
Microarray Types and Probe Density
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cDNA arrays: Robotically spotted PCR-amplified gene fragments (500-5000 bp).
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Oligo arrays: In situ synthesized 25-mers (e.g., 1.3M features on human chips).
Both contain large numbers of ssDNA for genome-wide screening.
GATE Biotechnology Relevance
Tests hybridization principle: ssDNA arrays vs. dsDNA irrelevance. Key for molecular diagnostics, cancer profiling, drug discovery questions.
