Backcross Breeding

Leah Sandall, Presenter Author

10/11/2018 Added

2361 Plays

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Although the transgene is put into a soybean plant in the plant transformation process, the variety used for transformation is not the 'latest and greatest.' In order to get the transgene in the very best varieties that farmers want to grow, breeders must cross the transgenic plant with the 'best or elite' variety. They continue to cross 'back' to the elite variety for several generations. The end result is the elite plant with the transgene added.

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[00:00:06.680]Backcross breeding
[00:00:07.560]is one of the steps in the genetic engineering process.
[00:00:10.680]So let's take the next few minutes
[00:00:12.530]to look a little bit more in depth
[00:00:13.920]at the process of backcross breeding.
[00:00:17.610]So one of the first things that happens
[00:00:19.670]after the genetic engineer
[00:00:21.120]has inserted the specific gene
[00:00:24.110]into the plant successfully, a transgenic line is produced.
[00:00:30.360]Keep in mind that the transgenic line
[00:00:32.500]is developed from plants that are standard lines
[00:00:35.620]that are used for transformation,
[00:00:37.120]and they're used, their standard lines
[00:00:39.190]are used because of a particular reason.
[00:00:42.330]So maybe they are hardier,
[00:00:44.080]they're easier to transform perhaps,
[00:00:47.460]maybe they grow better once they're on the media
[00:00:50.570]after transformation has occurred,
[00:00:52.440]and so these transgenic lines, then,
[00:00:55.085]will be used in the backcross breeding process
[00:01:00.300]by the plant breeder.
[00:01:03.170]And so once that transgenic line has been developed,
[00:01:05.736]then it's going to be crossed with an elite line.
[00:01:09.690]And the elite line is going to be that corn line
[00:01:12.740]that has many high quality traits
[00:01:15.150]that the plant breeder as well as producers
[00:01:17.810]are gonna be looking for.
[00:01:22.430]And so the first step that has to happen
[00:01:25.210]is an inbred transgenic line needs to be produced.
[00:01:28.755]And so that's going to happen by self pollination.
[00:01:33.689]And the seed on the ear is going to be,
[00:01:38.840]excuse me, is going to have two copies of the Bt gene,
[00:01:43.200]once the seed is harvested.
[00:01:46.278]And so both the transgenic inbred seed
[00:01:50.630]as well as the elite inbred
[00:01:52.480]will be planted side by side.
[00:01:56.230]And then cross pollination will occur
[00:01:57.860]from taking the pollen from the inbred
[00:02:00.530]transgenic line and placing that pollen on the ear
[00:02:04.790]of the elite inbred, and that's called cross pollination.
[00:02:10.660]So then the plant breeders will know
[00:02:12.280]that this ear on the elite inbred
[00:02:14.890]will have one copy of the Bt gene,
[00:02:17.270]or target gene that we're talking about in this example,
[00:02:19.990]and then it will have 50% elite genes
[00:02:22.790]as well as 50% non elite genes.
[00:02:28.680]So in order to continue
[00:02:29.890]to get those high quality traits that are desired
[00:02:32.850]plus the Bt gene, the next thing that will happen
[00:02:35.470]is the F1 plant, that seed will be planted
[00:02:38.830]and the plants grown, and it will be backcross, then,
[00:02:41.960]to the elite inbred, and that occurs
[00:02:43.820]by taking the pollen from that F1 plant
[00:02:46.770]and placing that on the ear of the elite inbred.
[00:02:49.940]And that process is called backcrossing.
[00:02:56.030]Then the seed will be harvested
[00:02:57.340]from that ear and it will have
[00:03:00.503]a copy of the Bt gene,
[00:03:02.310]and it will also have, then 75% of the elite
[00:03:04.913]or high quality genes that we're looking for.
[00:03:10.515]And again we're gonna plant seed,
[00:03:11.510]so we'll plant the backcross one seed,
[00:03:14.170]as well as the elite inbred seed again.
[00:03:20.630]And again we will do some backcrossing
[00:03:23.550]by taking the pollen from that backcross one plant
[00:03:26.640]and placing it on the ear of the elite inbred.
[00:03:31.510]So this same process will happen
[00:03:33.050]for about five or six generations
[00:03:35.065]until about 98% of the elite genes
[00:03:39.060]are gonna be present in that elite inbred
[00:03:42.810]along with the Bt gene.
[00:03:44.700]And so then through the process of selection,
[00:03:47.380]then the plants that are most desired
[00:03:49.820]by the plant breeder, that include the Bt gene
[00:03:52.160]and those elite genes, the high quality traits
[00:03:55.120]will be selected then by plant breeders
[00:03:57.110]to be grown by producers.
[00:04:03.780]So the only negative effect that this backcrossing process
[00:04:06.670]causes is something called yield lag.
[00:04:09.590]And what that means is that during the time
[00:04:12.160]that this transgenic line is being backcrossed
[00:04:15.422]in order to make sure that you're incorporating
[00:04:18.200]the new gene, plus all those high quality
[00:04:21.740]traits from the elite line,
[00:04:23.450]then other plant breeders are also continuing
[00:04:26.590]to develop new elite lines,
[00:04:28.060]and so that's where the yield lag is gonna come into play.

Backcross Breeding

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Backcross Breeding

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