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Duration:06:48
Uploaded:2021-09-23
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Strawberries are delicious, but for a molecular biologist, they're also very difficult.

Hosted by: Hank Green

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Sources:

Encyclopedia Britannica “Polyploidy” https://www.britannica.com/science/polyploidy
Nature SciTable “Polyploidy” https://www.nature.com/scitable/topicpage/polyploidy-1552814/#
Hardigan et al. 2020 “Genome Synteny Has Been Conserved Among the Octoploid Progenitors of Cultivated Strawberry Over Millions of Years of Evolution” https://doi.org/10.3389/fpls.2019.01789
Liston et al 2019. “Revisiting the origin of octoploid strawberry” https://www.nature.com/articles/s41588-019-0543-3
Edger et al 2019. “Reply to: Revisiting the origin of octoploid strawberry” https://www.nature.com/articles/s41588-019-0544-2
Zhang et al 2019 “Plant Polyploidy: Origin, Evolution, and Its Influence on Crop Domestication” https://www.sciencedirect.com/science/article/pii/S2468014119301980
https://www.genome.gov/Pages/Education/Modules/StrawberryExtractionInstructions.pdf
https://www.gardeningknowhow.com/edible/fruits/strawberry/growing-strawberry-runners.htm#:~:text=What%20are%20Strawberry%20Plant%20Runners,dry%20up%20and%20shrivel%20away
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4374564/
https://link.springer.com/article/10.1007/s11295-014-0773-6
https://www.nature.com/articles/s41438-020-0252-1#:~:text=The%20cultivated%20strawberry%20(Fragaria%20%C3%97,sensory%20qualities%20and%20health%20benefits
https://www.nature.com/articles/43815
https://www.journals.uchicago.edu/doi/abs/10.1086/285130?journalCode=an
https://blogs.scientificamerican.com/artful-amoeba/for-plants-polyploidy-is-not-a-four-letter-word/
http://www.adfg.alaska.gov/index.cfm%3Fadfg%3Dfishinggeneconservationlab.triploid_trout
https://www.scienceworld.ca/stories/how-do-seedless-watermelons-get-way/#:~:text=Seedless%20watermelons%20are%20triploid.,male%20with%20a%20tetraploid%20female


Images

https://www.istockphoto.com/photo/vd700-straberry-blossom-gm1054095518-281645742
https://www.istockphoto.com/photo/straberries-plant-propagation-gm503838630-82798931
https://www.istockphoto.com/photo/sago-palm-or-cycas-in-an-very-old-kind-of-tree-gm1212324905-351898573
https://commons.wikimedia.org/wiki/File:Karyotype_of_nine-banded_armadillo.png
https://www.istockphoto.com/photo/fresh-strawberries-background-gm477834644-66944023
https://www.istockphoto.com/photo/fresh-watermelon-pieces-gm96768336-6866718
https://www.istockphoto.com/photo/human-chromosomes-illustration-gm628915424-111768335
https://www.istockphoto.com/photo/delicious-fruit-salad-on-a-plate-on-table-gm1298307574-391190281
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Go to HelloFresh.com and use the code SCISHOW14  to get 14 free meals, plus free shipping! [♪ INTRO]. Most animals have two sets of  chromosomes. That’s nice for them.

It’s neat and tidy. Makes sense. And then there’s plants.

It turns out it’s super common for  plants to play around with polyploidy, the technical name for having more  than two full sets of chromosomes. Even in the food we eat. Maybe  especially in the food we eat.

So in this episode, we’re going to talk a  little bit about the what, why, and how. You’d never guess just from looking at them, but potatoes can have four sets of chromosomes. That’s known as 4n - n for “number of copies”.

Kiwis can be 6n, and strawberries…. Strawberries are 8n. Let’s quickly recap what exactly that means.

In plants and animals, our  DNA isn’t one long string, but instead it is packed into  discrete units called chromosomes. And we usually have two copies of each chromosome, because we inherit one copy from each parent. Polyploidy means going above and  beyond that very logical system.

This can sometimes happen in  animals, but it’s generally more of a genetic accident than a life strategy. A lot of the time, when animals  are polyploid, they’re triploid, meaning 3n: three sets of chromosomes. But that’s a problem, because it  generally makes that animal sterile.

Three is an odd number, and cells can’t  split three sets up evenly when it comes time to make sperm and egg cells, so  those cells end up failing at their basic job of passing on the genome. This is actually how seedless  watermelons are made. We intentionally create triploid watermelons.

But for a lot of plants, polyploidy isn’t  just a one-generation accident. It’s built in. With even numbers of copies, like  4n or 6n, they can not just survive, but reproduce and create whole  polyploid lineages and species.

In fact, all plant species  may have some episode of genome duplication in their past. Sometimes the plants keep their  new copies, like strawberries. Other times, they edit things back down to 2n, keeping some versions of their  genes and ditching others.

But all plants seem to have  done this at some point. As for how plants can get away with  this when animals generally can’t? It’s not entirely clear.

It’s been suggested that it might have to do with how plants and animals control their chromosomes. Many animal species tightly  control the “dose” of information coming from each chromosome. Like, mammals who have two  X chromosomes only need one.

So they turn the other one off. Whereas plants might not have to worry about it. Or maybe it’s because plants have  more flexible body plans than animals.

We have to have our arms and legs just so,  but plants can just sort of have a leaf, and then another leaf, and then  another one somewhere else. But it’s not just something  plants can get away with. Polyploidy seems to confer  some genuine advantages.

Having multiple copies of a gene might make harmful variants of that gene  less problematic, for instance. But the really cool part is  that extra copies of genes can be kind of a blank slate for evolution  to play around with over time. With other copies of those genes still  doing their thing, the extra copies of genes are then free to change  things up and acquire new functions.

It’s like turning a spare bedroom into an office. Over time, this could even lead to new species. And it might actually be related to  plants recovering from mass extinctions.

The timing of these duplication  events in plant genomes seems to correspond closely with extreme  changes, disasters, and mass extinctions. Polyploidy may have provided an advantage  in the form of increased adaptability. Or it may have hitched a ride with a  different trait, like asexual reproduction.

It’s been suggested that asexual  reproduction makes polyploidy more likely. And in the aftermath of a mass  extinction, not needing to find a mate before having babies might have been  a winning strategy in harsh times. Strawberries, for instance, can reproduce  via seeds, but also via runners, which result in clones of the parent plant.

That said, there are potential  disadvantages to polyploidy. More copies of chromosomes means more DNA, and that makes the nucleus of the  cell, which houses the DNA, bigger. And that can cause problems.

Like, it’s just generally harder to  find the right gene in all of that mess. There might also be problems with gene regulation, since suddenly doubling things can throw  the balance of the cell out of whack. So what does this mean for your strawberry torte?

Well, it turns out strawberries are  as difficult as they are delicious. Even molecular biologists admit they  are notoriously complex to study. Part of the reason is that eight  copies of chromosomes is just, like, a lot to deal with as you’re doing science.

Literally; it’s hard to tell one copy of  a chromosome from its seven other buddies. Trying to piece together their genome can  be a bit like sticking eight copies of. Hamlet into a blender and  then trying to figure out where all the “thees” and “thous” go.

This makes answering the question  of why they have eight copies, what specific event or factor led to  this genetic traffic jam, kind of hard. Nevertheless, there has been a  good amount of progress lately. And it looks like our modern strawberries  are a hybrid of naturally octoploid species, further tweaked by  domestication in the roughly 300 years or so of mass strawberry consumption.

So while domestication can be linked to  polyploidy, it turns out strawberries may have been as weird as they are  long before we got our hands on them. Anyways, while we are still looking for  the secret to the strawberry riddle, this is kind of a cool subject to  dive into generally, as studying the genetics of plants can help us  fight diseases or create new varieties. It’s also a cool reminder  about the diversity of life.

It’s pretty easy to get caught up  with how weird and wonderful and wacky animals are and to think the other kingdoms  of life are just kind of the background. But fungi, microbes, and, yes, even the  humble strawberry are just as strange and wonderful as any other organism on Earth. Thanks for watching this episode, and thank you to.

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