DNA Testing Overview

Grace Troupe, Presenter Author

10/11/2018 Added

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DNA testing is used to determine which plants to keep in a breeding program to ensure the transgene is carried through each generation. This video gives a brief overview of how this is done.

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[00:00:06.510]Good work, you made it through
[00:00:07.550]the final step of genetic engineering.
[00:00:09.980]So in this video we're gonna see where the gene has been
[00:00:12.700]and then get a brief overview of DNA testing.
[00:00:15.680]So we started our journey in Madan's lab
[00:00:17.870]where he designed the transgene
[00:00:19.380]by putting a soybean promoter on the Arabidopsis gene
[00:00:23.030]to turn it on in the roots of soybean.
[00:00:25.890]He then sent this transgene over to Shirley
[00:00:28.166]who got it into the genome of soybean plants
[00:00:31.192]through plant transformation.
[00:00:33.860]Shirley then sent these soybean plants with the transgene
[00:00:37.730]to George and he bred them into elite lines
[00:00:41.170]that farmers actually want to grow.
[00:00:44.060]So now George works with Justin
[00:00:47.100]who at every generation lets him know
[00:00:49.890]whether the transgene
[00:00:51.120]is in the lines that he's working with
[00:00:53.080]because if the transgene isn't there
[00:00:54.680]he wants to get that plant out of his breeding program.
[00:00:58.530]So Justin's goal in DNA testing
[00:01:03.950]is to determine which plants carry the transgene.
[00:01:07.400]Any plants that don't we wanna throw out
[00:01:09.320]of the breeding program, because our end goal
[00:01:11.250]is to get that plant that has that new trait
[00:01:13.789]caused by the transgene.
[00:01:17.610]So he does this in three different steps,
[00:01:19.900]and the first one is extracting the DNA.
[00:01:22.720]In order to see if the transgene is there
[00:01:24.220]we need to get the DNA out of the plant
[00:01:26.340]so we can look at it,
[00:01:27.780]and this looks a little bit different
[00:01:29.690]than the way Madan did it, right?
[00:01:32.170]Justin's using these big machines.
[00:01:34.149]And that's because there are thousands of plants
[00:01:38.960]that a breeder is working with at any given time
[00:01:41.890]and if we need to look at the DNA
[00:01:44.550]in all these different plants,
[00:01:46.270]then we need to be able to scale up this process
[00:01:48.580]and look at a lot of DNA at once.
[00:01:50.910]So Justin uses a lot of these bigger machines
[00:01:53.250]to do the same thing as what Madan was doing
[00:01:55.630]extracting the DNA and looking at it.
[00:01:59.630]But he can do a lot more at once using these tools
[00:02:02.550]so that's why it looks different.
[00:02:06.000]So next Justin uses PCR to make copies of the gene.
[00:02:11.400]And so why does he really want copies of this transgene?
[00:02:15.710]Well the reason is we can't see one gene at a time.
[00:02:20.630]So in order to tell if the transgene is there
[00:02:22.680]we need to make enough copies that we can see it.
[00:02:26.890]So there's two options, let's say we got this plant,
[00:02:30.720]we collected tissues from it in the field,
[00:02:33.030]one is that it is a transgenic plant.
[00:02:35.070]It does still have the transgene.
[00:02:37.530]But the other option is that when it was bred
[00:02:40.640]in this last generation, it didn't inherit the transgene,
[00:02:43.730]and so it's nontransgenic.
[00:02:46.130]So we only wanna keep transgenic plants.
[00:02:49.389]So with PCR we can decide
[00:02:51.650]what section of the DNA we wanna make copies of.
[00:02:54.880]And you can use these things called primers,
[00:02:57.040]so that way you can only make copies
[00:02:59.330]of just one piece of DNA
[00:03:01.970]and so we make copies of only the transgenic region.
[00:03:05.920]So what would that look like?
[00:03:07.180]How would that be different between these two plants?
[00:03:10.150]Or these two options?
[00:03:12.008]Well if you're only copying the transgene
[00:03:14.093]if it's a transgenic plant, you're gonna get
[00:03:17.260]billions of copies of this transgene in your test tube.
[00:03:23.250]But if it's a non transgenic plant
[00:03:26.376]there's gonna be nothing to copy right?
[00:03:29.360]If you're only copying the transgene region,
[00:03:31.317]and there is no transgene region,
[00:03:34.360]you're gonna have an empty tube.
[00:03:35.730]Right?
[00:03:37.268]Just the original DNA, and so your test tubes
[00:03:41.230]will we very different, but these pieces
[00:03:43.690]of DNA are so small that when you look
[00:03:46.160]at them with your naked eye,
[00:03:47.200]they're gonna look the same to you.
[00:03:49.530]So now we need a way to distinguish these,
[00:03:52.510]even though they're different,
[00:03:53.913]you can't see it with your eye.
[00:03:56.281]So that's why we use gel electrophoresis.
[00:04:00.870]It lets us see what's in those tubes.
[00:04:03.893]So let's, what this is, gel electrophoresis
[00:04:08.420]this is like a thick piece of Jello
[00:04:11.130]and at the top we have a hole at the top of each lane.
[00:04:15.710]So this is where you pipette the contents
[00:04:18.930]of each of those tubes, and we have five different holes,
[00:04:23.960]we call them wells, so right here
[00:04:26.250]we're looking at the results for five plants.
[00:04:30.390]And this over here just tells us
[00:04:32.674]a rough estimate of the size
[00:04:34.492]of the different pieces of DNA.
[00:04:37.911]So I want you to pause this video
[00:04:42.280]and take a guess at which plants
[00:04:45.340]you think have the transgene.
[00:04:50.315]Alright, so there can only be something in the lane
[00:04:56.090]if there is DNA there.
[00:04:58.470]We put a fluorescent dye that binds to the DNA
[00:05:01.710]and it'll glow if there's DNA in that well,
[00:05:05.200]or in that lane.
[00:05:06.667]So these first two plants, since there was nothing to copy
[00:05:11.669]'cause there was no transgene,
[00:05:13.340]there's no band, so those are nontransgenic,
[00:05:16.930]and we'll wanna throw those outta the breeding program.
[00:05:19.818]Three, four, and five, however,
[00:05:22.000]have these bands and this is representing
[00:05:27.160]those billions of copies of DNA,
[00:05:30.050]so we got them to this point in the gel
[00:05:32.370]by pulling it through with electricity.
[00:05:34.770]And then when we put this over UV light
[00:05:36.670]we could see that all these copies are here.
[00:05:38.920]And so we know that these plants have that transgene
[00:05:41.114]so we'll keep those in our breeding program.
[00:05:45.259]Alright so that's what Justin does
[00:05:47.540]to help George know which plants to keep.
[00:05:49.965]And that's the process of genetic engineering.
[00:05:53.917]And I wanna remind you that throughout this whole process
[00:05:57.870]there's lots of safety testing and regulation
[00:06:00.581]that each of these scientists has to go through
[00:06:03.350]and if you want to learn a little bit about that
[00:06:05.948]go back to the home page,
[00:06:07.870]scroll to the bottom,
[00:06:08.730]and click risks and benefits,
[00:06:10.570]and we have a little bit of material
[00:06:12.230]to help you learn some of those different steps
[00:06:15.150]that help us know whether these products are safe for us.
[00:06:19.610]Thanks for going through the journey of a gene!

DNA Testing Overview

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DNA Testing Overview

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