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Examples: rDNA, mRNA, tRNA.

Why do we use small case for "r" in "rDNA", etc? Any particular reason?

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    $\begingroup$ I’m voting to close this question because it is about the history or philosophy of coining abbreviations/acronyms rather than a problem in biology. $\endgroup$
    – David
    Nov 24 at 11:00
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It's just a stylistic approach because "DNA" or "RNA" is an abbreviation by itself that has become a whole noun. Those terms clearly separate the modifier from the overall DNA/RNA. It makes it easier to read. Terms like DNA and RNA are almost always known just by those acronyms, whereas something like mRNA is known both as "messenger RNA" and "'m' RNA" but almost never as "messenger ribonucleic acid."

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These letters are used to indicate the different types of RNA and DNA. Especially RNA has lots of (functionally) different variants, so this helps discering between them.

Your exmaples in particular: - mRNA is short for messenger RNA - tRNA is short for transfer RNA - rDNA could be ribosomal or recombinant DNA (writing rDNA is very uncommon, mostly ssDNA or dsDNA are used)

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    $\begingroup$ "For DNA this way of writing is very uncommon." Nope. I often read ssDNA (single-stranded DNA) or dsDNA (double-stranded DNA) or mtDNA (mitochondrial DNA) etc.. $\endgroup$
    – adjan
    Jun 9 '17 at 7:39
  • $\begingroup$ @adjan Ah true I didn't think about that, I edited the answer. rDNA is still uncommon though ^^ $\endgroup$
    – Nicolai
    Jun 9 '17 at 7:56
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    $\begingroup$ I don't agree with that minimized claim, either! I see rDNA used all the time in scientific papers, textbooks, and even informal literature. While it's true that the abbreviation is problematic because of the ambiguity, it is usually pretty clear from context whether they mean "ribosomal" or "recombinant". $\endgroup$
    – Cody Gray
    Jun 9 '17 at 9:23
  • $\begingroup$ The poster didn't ask what the abbreviations meant, he asked why lower case. $\endgroup$
    – David
    Nov 24 at 11:02

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