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Viruses can be fairly complex, but imagine the very basic form of what they are: A string of DNA floating around and getting into cells, and causing them to produce more copies of itself. Obviously viruses are more than just rogue DNA, but that's their function - they corrupt other cells. They don't eat, photosynthesis, reproduce, etc. They're much closer to a chemical reaction, like how fire causes wood to create more fire, except orders of magnitude more complicated.

When you hear "consume" or "metabolize", it doesn't just mean destroying or altering a molecule. The important bit is that energy is removed from the molecule and used by the "organism" in question. Fire definitely does count for that particular one, as the reaction to burn something is almost exactly what we do in our bodies. We burn our food, just much more slowly. A prion though, does not meet that criteria. It does alter a molecule (the non-dangerous form of the prion protein), and energy is removed (the dangerous form of the prion is at a slightly lower energy level, I believe), but the original prion doesn't do anything with that energy. It is unchanged.

I didn't hear of something like that, but think it's possible.

If you remember or find the info it would be interesting to know.

TIL! Thanks :)

I actually had to look some infos up again and found another fun (?) fact.

In South America there are nine species of vole (genus Akodon) in which a quarter of female are XY, not XX. Their Y chromosome is complete with SRY, yet they still develop ovaries and produce viable eggs. That suggests they must have a entirely new master switch gene that can suppress SRY.

Hmmm, perhaps what I'm thinking is that multiple different male chromosomes have evolved in different branches of evolution?

I don't know about that. I'm referring to J. M. Graves, a professor of evolutionary genetics. She looked at how the platypus Y was different to the human Y and calculated how much genetic material had been lost since our species diverged. That's how she got that time frame.

But she also told that some (male) scientists aren't fans of this and try to prove how stable the Y chromosome is.

I honestly think that most microbial stuff (prions, viruses, even bacteria to some extent) is closer to machinery than anything a layman would consider "life."

Sure, it's autonomous self-replicating machinery that actively seeks and processes its own fuel, but... well, you could design a macroscale machine that does this.

You wouldn't want to, because you'd be Ted Faro, but it's possible.

There are several measurable differences between cells and viruses.

Defining what viruses are, and thus whether or not they're considered "life", is quite scientifically important. We need to define things based on what their uses and limitations are. Viruses are already known to have unique characteristics; if we further define those characteristics and are able to distinguish them from organisms, we can potentially discover new things about life, or new things about almost-life as a whole that fits certain parameters. We dont know what we don't know. Everyone freaking out over labels is missing the point, as usual.

SRY is like a conductor. It triggers the multiple genes to express testes or suppress ovaries. But those genes also trigger and suppress other genes. And while SRY is the trigger in some mammals, it's not necessary to kick start sex determination.

For example the platypus has five pairs of sex chromosomes. Females are XXXXXXXXXX and males are XXXXXYYYYY. Despite that many Y, on none of them SRY is found. One of those other interacting genes triggers sex determination. What's even more interesting those various involved genes can be found in similar combination throughout all vertebrae, but the trigger differs.

So while SRY is the trigger in some, it's not the only one.

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Sometimes SRY gets copied onto the end of an x chromosome during meiosis. People who inherit this end up as xx males.

> they could potentially go even further, if there are genes sets where knocking out only single components was lethal, but knocking out the whole set was survivable, so there's potential to go even further.

That’s got to be maddening, having to account for various combinations within your original problem.

This probably gets into more philosophy than science maybe, but there's not really a clear-cut line between "life" and "non-life" which is why it's hard to classify where viruses fall. If you instead think of life as less of a binary state and more like a process of self-preservation/self-propagation, then viruses certainly fit that bill. I would imagine the usage of the term "organism" predates thinking of life as a process and more of a state.

There doesn't have to be any fundamental measurable difference between something that is or is not life. Reality doesn't really care about our need to define things.

The poster is referencing deltavirus, which also doesn’t produce its own capsid. Its only not a viroid because it steals a capsid from HepB.

You have a version of these within your genome as well. Look up retrotransposons and other genetic mobile elements.

If there is a virus that can self-replicate, that's news to me. Which viruses do that?

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I mean, sure. Maybe such a thing exists, but if we don't know of that, we're just making things up.

Not that it matters, but I don't personally draw a line between a bunch of molecules and an animal. Granted, that's not a common opinion

I get the edges are very blurry when defining what something is or isn't in biology, but I wouldn't equate destroy or alter with consume, or grow with reproduce, either.

I think the answer lies in quantum physics, we may find some mechanism there that exists in typical life but doesn't exist in atypical thing like viruses and self-replicating RNA. Either that, or it lies in chemistry and we just haven't found the right experiment to make the discovery with. Because the line between "a mix of compounds/elements that can do complex things" and "life" has to be drawn somewhere right?

I seem to recall learning somewhere that the male chromosome has been seen to disappear as you described, and then reevolved again later on in the same species (or perhaps one of its evolutionary offspring species so to speak). Is this true?

Behold, a man!

But yes, examples like fire (nice idea on that one btw) are why "life" is weirdly tricky to define.