Question

Which is incorrect with reference to transposon?

• A. It is known as jumping genes
• B. It was first discovered by Barbara McClintock
• C. Retrotransposons can move through RNA intermediates
• D. 2/3 of human genome is made up of transposons

Hint:

• Transposons ("Jumping Genes") Mobile DNA elements.
• Discovered by Barbara McClintock in maize.
• Class I (Retrotransposons) Move via an RNA intermediate (copy-and-paste). E.g., LINEs, SINEs, LTR retrotransposons.
• Class II (DNA Transposons) Move directly as DNA (cut-and-paste or replicative transposition).
• Transposons constitute a large fraction of many eukaryotic genomes (e.g., ~45-50% in humans).

Answer 1

The Correct Option is D

Transposons (transposable elements or "jumping genes") are DNA sequences that can change their position within a genome, either by a "cut and paste" mechanism (Class II transposons, DNA transposons) or via an RNA intermediate ("copy and paste" mechanism, Class I transposons, retrotransposons). Let's analyze the statements: (a) "It is known as jumping genes": TRUE. This is a common informal name for transposons due to their ability to move within the genome. (b) "It was first discovered by Barbara McClintock": TRUE. Barbara McClintock discovered transposable elements in maize (corn) in the 1940s and 1950s, for which she received the Nobel Prize in Physiology or Medicine in 1983. (c) "Retrotransposons can move through RNA intermediates": TRUE. Retrotransposons (Class I) move via a "copy-and-paste" mechanism that involves transcription of the retrotransposon DNA into an RNA intermediate, followed by reverse transcription of this RNA back into DNA, which then inserts at a new genomic location. (d) "2/3 of human genome is made up of transposons": FALSE. Transposable elements and their remnants make up a very significant portion of the human genome, estimated to be around 45% to nearly 50%. However, 2/3 (which is approximately 66.7%) is an overestimation. While substantial, it's not quite that high for sequences directly derived from or identifiable as transposons. Therefore, the incorrect statement is (d). \[ \boxed{\text{2/3 of human genome is made up of transposons}} \]