Hello, please tell me about corn genetics

botanyshitposts:

botanyshitposts:

maize. 

maize is so fucking weird. like i can’t even cover it in one post so i’m just gonna focus on one of the LARGEST reasons it’s so fucked up in this post so buckle in babes it’s time for a wild ride

to understand maize genetics on a fundamental level, we have to understand the work of Dr. Barbara McClintock, a brilliant botanist who dedicated her life to how fucked up corn is while simultaneously never being taken seriously because she was a woman. McClintock noticed a few things while studying maize in the early 1940s. as you might know, maize doesn’t always look all yellow; sometimes the kernels are colored differently, like this: 

well yeah about that, she started noticing correlations in how the kernels were colored based on certain cases of the genes (imagine them as sections of DNA) she was looking at being rendered nonfunctional (or being “broken”).

for instance, lets say we breed a maize plant thats supposed to have only purple cobs, but when it grows up, the cobs are a different color entirely, or patterned differently, or completely different from what we were expecting. this happened a lot to McClintock. like, constantly. after testing the DNA of the plant, she would find that the reason the plant didn’t bear purple cobs was because of other genes randomly teleporting into the middle of the gene she was testing for. so our purple maize plant wouldn’t make purple cobs because some random ass shit inserted itself in the actual fucking middle of the ‘make purple pigment’ gene, causing it to ‘break’. we now know these teleporting little shits as “transposons”, and they’re a normal thing that casually happens IN ALL LIVING THINGS. but they didn’t know that in the 1940s. 

so not only did McClintock have random shit jumping into other random shit, but she had a REALLY hard time on her primary project of mapping the maize genome (the act of building a basic outline of which gene goes where on each chromosome) because it seemed like no matter what gene she was looking at, it would be in a different place in the genomes of all her plants (it should be noted that as we know them to be, many genes really are stable and stay in their same positions consistently through a species. for instance, lets say that there’s a gene on your 5th chromosome that codes for eye color. although your eye color may be different than the person next to you, their eye color gene is still located on the 5th chromosome; the code is just different. in McClintock’s case, NOTHING was staying consistently ANYWHERE between multiple samples of corn). 

so McClintock was like, “hey uhhhhh these genes can jump wherever and the genome isn’t actually a stable consistent thing that we’re born with like we’ve thought it was up until now. like it turns out an organism’s genes can change over the course of its life responding to different environmental pressures, and part of how DNA accomplishes this is through making these weird jumping genes change positions when the organism is exposed to certain things.” 

this was a BIG mistake. she continued to publish her results for the next 15 years until she got so much hate she had to stop publishing the evidence she found not only for the existence of transposons, but her theories as to why they were there and what purpose they serve. other scientists in her (primarily male) field of experimental genetics REFUSED to believe this from her until nearly two decades later, when two male scientists- fellow biology students may recognize the names Francois Jacob and Jacques Monod, who worked with confirming the regulation of the lac operon and are still considered the fathers of epigenetics despite you know, not actually being the fathers of epigenetics since she did it twenty years earlier and i personally refuse to worship their shitty ass milk triumph- confirmed that genes could be, you know, regulated, and that the genome could be changed over the course of your life and that transposons were VERY MUCH possible and were also rediscovered in the following decade in similar encounters. anyway she casually won the nobel prize for her work in 1983, literally 40 years after she discovered it when everyone realized that she had been right all along and that they’d been belittling her and shitting on her for decades over it lol. 

anyway, all that aside: why is corn weird? why did it take until literally 2009 for us to map the maize genome for the first time? 

well here’s the kicker: 

the maize genome is 70-85% transposons or transposon-like elements depending on which variety you choose. 

70-85% of the genome of maize, in it’s natural form, literally does not stay in one place between generations. it just doesn’t. it fumbles around and breaks shit CONSTANTLY when exposed to different things. its an actual trainwreck in a constant state of slamming shit into other shit until shit happens. like given, plants in general have weird genomes and like, i can understand that and accept that, but this is actually fucking ridiculous. to put this in perspective, roughly 44% of the human genome is transposons or transposon-like elements. take that amount and double it and you have about the same amount of genomic chaos as maize. i’ve said it before and i’ll say it again: 

the maize genome is a goddamn build-a-bear workshop and it scares me

EDIT: @thecrystalmadness brought up a good point in the tags that the source study for the percentage of the human genome statistic points out that although 44% of the human genome is structurally transposons, less that 0.05% are considered by the study to be active elements, which reflects how I need to be sure I’m reading all the sources I reference, not just the plant-related ones is a really interesting idea when we think about the maize genome; maybe the reason the maize we look at now is remotely consistent is because many of them have long since been disabled or silenced? 

I tried digging a bit to see if I could find a similar study on general activity for Maize and didn’t find anything outside specific studies on families of genes, but let’s not forget that the maize genome has an entire database just for its transposons. In the intro, the database notes that the Maize is, “recognized as having the most dynamic TE component,” of most, if not all, higher eukaryote organism and that “As such, it is the organism of choice for understanding how TEs contribute to gene and genome evolution”. so whatever that number of active elements is, it’s significant enough to have affected how the species responds to many different kinds of evolutionary pressures and is indeed quite, how do u say, fucking high and very intimidating