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Biology Question 120 – NEET-UG 2023

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Expressed Sequence Tags (ESTs) refers to

Expressed Sequence Tags (ESTs) are short, single-pass sequences from a cDNA clone that are used to identify gene transcripts.

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Ninja Strategy•Definition Recall

The name 'Expressed Sequence Tags' itself provides a strong clue that these tags relate to genes that are actively 'expressed' as sequences, primarily RNA.

Step 1: Define Expressed Sequence Tags (ESTs)✦ Active

Expressed Sequence Tags (ESTs) are short, single-pass sequences from a cDNA clone. They are used to identify genes that are actively expressed in a particular tissue or at a specific developmental stage.

Step 2: Relate ESTs to Gene Expression○ Expand

cDNA (complementary DNA) is synthesized from mRNA (messenger RNA) using reverse transcriptase. mRNA molecules are the direct products of gene transcription, meaning they represent genes that have been expressed as RNA.

💡 Teacher's Secret Hint

Remember the central dogma: DNA → RNA → Protein. ESTs capture the RNA stage.

Step 3: Evaluate the Options○ Expand

Based on the definition, ESTs directly reflect the genes that are transcribed into RNA. Therefore, option (1) 'All genes that are expressed as RNA' is the correct description. Option (2) is incorrect because not all RNAs are translated into proteins, and ESTs directly reflect RNA. Option (3) is incorrect as ESTs specifically target *expressed* genes. Option (4) is incorrect because ESTs aim to identify all expressed genes, not just 'certain important' ones.

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