I ran into a joke recently and I need an explanation in regards to this term. It was originally a twitter post that was reposted to a meme site that I browse.
-Studying for exam in college-
Me: reading notes: ‘tetrahymena thermophila are free-living
pond ciliate which have a macro-nuclear draft genome of 180
chromosomes and 25,000 genes’
Me in my head “yah most of this is pretty much common sense
anyways”
-goes to sleep
Basically other then the ‘macro-nuclear draft genome’, most of this makes sense – and google searches do render the term as a legit term (however no even half decent explanation of what it actually is).
Keep in mind this was posted as a joke: So I’m also not sure if it’s just a word salad or anything like that – but I would like to know one way or another as it’s REALLY driving me bonkers.
Source of post: (NSFW warning for the site – funny junk): https://funnyjunk.com/Sudden+scared+admired+giraffe/XfaxMKs/
In: Biology
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I don’t see any actual answers here so I guess I’ll contribute:
“Macronuclear draft genome” isn’t all one thing, it’s a “draft genome” of a “macronucleus.”
In genomics, a draft genome is basically what it sounds like: it’s a “first draft” of a genome. A lab/researcher sequenced a certain organism’s genome, and since sequencers are not 100% accurate it still has some inconsistencies, gaps, etc. Draft genomes are published simply to contribute to the sequencing effort: it’s kinda like “here’s our first attempt at the genome. Y’all can take a look at it and compare it to what you got when *you* tried sequencing the genome.”
Through multiple repetitive sequencings, draft genomes slowly get their gaps filled in and their inconsistencies resolved, to form a final genome.
For example, if lab A got the following sequence:
AATTCCGG-[gap: we don’t know what goes here!]-AATTCCGG
and lab B got the following sequence:
[gap]-TCCGG-ATATATAT-AATTCCGG
The gaps don’t overlap. Between the two labs, they got the full sequence which is:
AATTCCGG-ATATATAT-AATTCCGG
So each lab published their “draft” containing some minor gaps, and by putting the two drafts together you get the final, whole genome.
Lab B provided the ATATATAT that was missing from Lab A’s draft, and Lab A provided the AAT that was missing from Lab B’s draft.
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So that address the “draft” part. What about the “macronuclear” part?
As you correctly guessed, this is a ciliate thing. Ciliates tend to have *macronuclei* which just means that instead of duplicating the genome and then splitting like normal cells, they duplicate their genome and *don’t* split.
So over time their nucleus accumulates many copies of the genome, since it keeps duplicating it but never splitting apart.
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So to answer your question, the “macronuclear draft genome” is one particular lab’s attempt at sequencing the genome found in the macronucleus of a ciliate. If multiple labs have sequenced it but it still has gaps, it remains a draft genome (so the draft genome in question may not be just one lab’s effort, it just means the sequencing work isn’t done yet)
Let me know if you need any clarification!
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