Questions about GMO, Corn Genetics and some Corn Pictures

[Joseph Lofthouse]

Pericarp color is a bit hard to select for, because it is a maternal only trait, so half of the seeds that carry the trait this year might not carry it next year if the mother is heterozygous for the trait. (And kernels can be carrying the trait this year, but it will only show up in the children.)

Backcrossing is typically only done with dominant traits, to move a single trait into another line of corn, so that the end result is like the original parent except with the addition of one trait. It could be done with recessive traits, but you gotta grow it out for a few years in between each backcross (or use DNA testing).

If you wanted to move Big Red's delicious pericarp into Painted Mountain while keeping Painted Mountain looking/acting as close as possible to it's current form....

Make the original cross: Use Painted Mountain as the pollen donor.
If Big Red is homozygous for delicious pericarp, and if it's a dominant trait, then all the offspring should show the trait. If it is heterozygous, then only half of the offspring will carry the delicious pericarp trait.

Plant seeds only from cobs that have that delicious pericarp. Detassel and use Painted Mountain as the pollen donor.
Repeat as necessary until the offspring look like Painted Mountain except for that one trait. The graphic shows that after 5 generations the genes are 97% Painted Mountain and 3% Big Red.

Then you need to do an additional 5 years or so of additional selection to get rid of the recessive traits for other types of pericarp that are inherent in Painted Mountain. (Or you need to do a single generation of selfing, and then grow out sufficient numbers of offspring to be able to eliminate the parents that carry genes for undesired recessive pericarp traits.)

I'm not so much of a purist as that, and downright lazy. I'd cross the two lines, and then select out of the jumble the plant families that are most appealing to me.

[philagardener]

Nov 26, 2014 19:25:18 GMT -5 reed said:

The graphic shows how each generation an F1 is crossed back to one of the parents the result has 1/2 of the previous parent, keep doing that until you have mostly the one parent left but with the trait you wanted from the other. Rather like a radioactive half life.

Good analogy.  When one wants to introduce a new trait like disease resistance into an inbred line, the rule of thumb among plant breeders is generally 7 generations of back-crosses to get roughly back to the strain you wanted plus the new trait.

Hope the dog came home!  **Glad you found her and she is OK!!!**

[reed]

Went back and edited the other post after the dog issue and realized I should have just done another post so here is the rest,I just copied it the other one.


****
I'm back. The bad news is she was caught in a leg hold trap in the neighbors hay field. Good news is she seems to be OK, nothing broken. Gave her some turkey giblets we used to make broth and she is in her bed, her mood is happy as ever. I can hardly believe I found her, logic said not to try till daylight but something said go look anyway, so glad I did.****



Back to this backcrossing thing. It occurs to me it is mostly useful when you know for sure a specific trait you want incorporated into a specific variety but what about if that isn't all or even the most important thing you want to do?



Might it not be more productive if your goal is more of a landrace to keep crossing the F1 with itself and letting conditions select for what works, especially if you have multiple different F1s with multiple combinations of mothers and fathers? Then after two or three years of that start selecting for flavors, uses, and other traits you like?

[reed]

Nov 26, 2014 21:26:12 GMT -5 Joseph Lofthouse said:

I'm not so much of a purist as that, and downright lazy. I'd cross the two lines, and then select out of the jumble the plant families that are most appealing to me.

I like that, I'm so glad you didn't say the backcrossing police would take me away if I didn't do it. 

[philagardener]

Different goals require different approaches.

In working with landraces, you grow lots and select continually for population characteristics in a diverse gene pool rather than single genetic traits or specific gene combinations. Diversity becomes your friend!

[reed]

My biggest goal is locally adapted things that I can count on to produce in less than perfect conditions so the landrace makes most sense to me. Wondering, why can't I just mix it up and keep the best, is how I found this forum. I was just plum tired of endless descriptions of the fine distinctions between this one and that one in the seed books. Especially since it was very rarely true. And, it takes a whole year to find out. Then, you get to star over...again. I'm done with it.

[reed]

Got some more pictures and questions about the big red ear. Not sure how I will use this except that I want to be sure I don't lose it. May decide to grow some separately from the rest next year just for insurance.

I thought I would sacrifice 10 more kernels to see what else I could learn about it and corn in general as far as homozygous vs heterzygous, gene dominance and things like go. 

First picture is just the ten chosen kernels. I figure 10 out of a total 600 should give a pretty good sample. 


Pericarp is all the same, I've learned that is because it maternal. I cant't tell from this however if it is homozygous or heterzygous. Now I'm trying to figure out the probability this pericarp will show up next year if crossed with something else (with this as mother) and if grown isolated by itself.

Next is the aleurone layer of the same kernels in the same order


Found a good amount of variation here in the aleurone layer, didn't really expect that. I suppose that means that this is not maternal and is also subject to even more variations because it can come from either parent. 

And the endosperm, again in the same order

Since I am partial to it I was happy to see 70% of the kernels are white. It apparently isn't related to the aleurone based on this observation and also not maternal. What should this tell me if anything about heterozygous or homozygous aspect for the endosperm color and probability of it showing up next year if only white is planted? 

Based on other reading I'm guessing one of this plants parents was homozygous for white and the other was heterozygous so it ended up 75% white???

Thanks to everyone who is helping me with this. I can use it for everything not just corn, and though I fully expect plenty of failures I'll have at least some idea of what is going on . It will save years of trial and error. 

 

[Joseph Lofthouse]

It is hard to make too many predictions, because the corn was grown in a patch and we don't know much about the pollen donors. Also in patches with a mixed genetic background, the manifestation of any particular trait might depend on multiple genes being present.

If the cob is homozygous for red pericarp and it is a single gene trait, then all of her children will carry the trait. If the pollen donors didn't carry the trait, then half of the grandchildren will lack the trait.

If the cob is heterozygous for red pericarp and it is a single gene trait, then if the pollen donors didn't carry the trait, half of the children will lack the trait.

You may be able to screen for this trait before the plants flower. Notice the tips of the kernels. They are red. That is usually associated with having red color in the stalks and/or leaves. So go through the patch early on and chop out any plants that have typical yellow stalks. Keep only the plants that have red in the foliage. (Or self pollinate by hand, or transplant to a semi-isolated bed. These options are more conservative.)

The corn was grown in a patch... The trait predictions commonly made using Mendelian genetics are for individual plants that are self pollinated. This cob was grown in a patch and it's hard to make predictions because we can be safe assuming that the mother was homozygous for white endosperm. But there could be as many as 600 fathers. It looks like many of the fathers also had the trait for white endosperm.

If you use a dissection technique that doesn't destroy the embryo, then before planting this spring you could select for white endosperm.

But if you just plant the seed... Then to select for (higher concentrations of) white endosperm, save the seeds as cob-to-packet. Then dissect about 20 seeds. If all or half of the seeds have yellow endosperm then don't replant seeds from that cob.

[oxbowfarm]

Another way you could use this ear to develop a white endosperm strain is to plant a short row from this ear and self the plants. Since it looks like you are getting about 70% white endosperm, it would be enough to self just 10 or so plants. A few of them would be sure to be white endosperm, so after harvesting the cobs you could check the endosperms and save all the white cobs. Then you'd have a strain you knew was white underneath the dark pericarp. You'd need to invest in some tassel and ear bags.

[reed]

Nov 28, 2014 12:07:30 GMT -5 Joseph Lofthouse said:

The corn was grown in a patch... The trait predictions commonly made using Mendelian genetics are for individual plants that are self pollinated. 

Yea, I kinda figured the other information I came across before I found this forum was based on situations dealing with less variables and where those variables are better understood and better controlled. Papers written by people with PHDs for people with PHDs and probably a lot of them never grew much of anything outside of a lab environment. I don't really mean to knock those folks (except about GMO), I'm just not in their target audience. Some of the old stuff like when they were making the Iowa Stiff Stalk lines was the best reading anyway and I guess since it was old I could have it all instead of just an abstract.

[reed]

Nov 28, 2014 16:10:10 GMT -5 oxbowfarm said:

Another way you could use this ear to develop a white endosperm strain is to plant a short row from this ear and self the plants. Since it looks like you are getting about 70% white endosperm, it would be enough to self just 10 or so plants. A few of them would be sure to be white endosperm, so after harvesting the cobs you could check the endosperms and save all the white cobs. Then you'd have a strain you knew was white underneath the dark pericarp. You'd need to invest in some tassel and ear bags.

Thanks, about the tassel and ear bags, could I get around that by planting a patch from this cob four hundred or so feet from anything else? I'm afraid this is longer season than the strain I want to develop so I need to grow it to find that out and to increase my supply of it genetics. I figure if I plant around a hundred or so of just the white ones off by itself that should secure it for future use. I could also plant fifty or so plants in the main patch but detassel it. That way I could find out its season length and (if it fits in OK) have a head start on mixing into the main crop. 

[oxbowfarm]

It wouldn't help to fix the white, because you still have 30% yellow kernels in the cob. So an isolated patch is still going to contain 30% yellow endosperm mother plants. When you self or hand pollinate then you know absolutely who the parents are for all the kernels. A white endosperm mother plant selfed will give you an all white endosperm ear. Its totally possible to fix white endosperm without selfing, but that corn is really difficult because you cannot see the endosperm. By far the easiest way to fix white would be to self some plants.

[reed]

I was thinking of doing like Carol said and use a file to make a little window on each kernel so I know that only white ones get planted. Or is it that a white one still has a 30% chance of growing yellow? And if a yellow one was in the patch, it would cross with the others and I'd still end up with white / yellow ears?

By selfing each individual (only white seeded) plant would I get 70% all white ones and 30% all yellow rather than a mix on each ear?

[oxbowfarm]

Dec 3, 2014 4:07:58 GMT -5 reed said:

I was thinking of doing like Carol said and use a file to make a little window on each kernel so I know that only white ones get planted. Or is it that a white one still has a 30% chance of growing yellow? And if a yellow one was in the patch, it would cross with the others and I'd still end up with white / yellow ears?

By selfing each individual (only white seeded) plant would I get 70% all white ones and 30% all yellow rather than a mix on each ear?

Filing the kernels would work too. If you open a window into each kernel and only plant white endosperm kernels in your isolation plot then you would be planting a 100% white endosperm group of plants assuming you didn't make a mistake identifying the endosperm color. The 70:30 ratio applies to the total population on your ear, not at the individual kernel. Each individual kernel is either white, homozygous yellow or heterozygous yellow. Selfing a white gives you white. Selfing homozygous yellow gives you yellow. Selfing heterozygous yellow gives you a 3:1 mix of yellow and white.

[Carol Deppe]

Nov 28, 2014 9:35:27 GMT -5 reed said:

Hi Reed--

I've eaten many a kernel with that deep red pericarp, and don't blame you for wanting more. In my experience, it takes homozygous red pericarp, white aleurone, and white flinty endosperm to get that mind-blowing flavor. Since red pericarp is variable in expression, there may well be additional modifying genes also required to get that deep red. So the color you want may well be associated with homozygosity for one dominant and two recessive genes at the least, possible more than two. You can't easily tranfer recessive genes to another variety by recurrent backcrossing. Furthermore, Painted Mountain isn't pure for any of these kernel color genes, including pericarp genes. 

Your kernels with the pericarp skinned off are showing a strange color. It could be lavender (Dominant Purple modified by recessive red-aleurone.) And that would also work, as lavender has a wonderful flavor parched. However, the color in your photos doesn't really look lavender to me. I suspect you have white aleurone that has been stained by the pigment from thepericarp. Pericarp red pigment is water soluble. 

I suggest you save half the kernels and plant the rest in a patch by themselves without filing or messing with them, and just increase the population. I'd increase the population before I tried to select the population to get rid of the yellow. What would be ideal would be if that ear has enough genetic heterogeneity in it so that you can produce a whole variety from it just by taking care to eliminate as little of the genetic heterogeneity as possible. So for that, you really need to plant as many kernels as possible next spring, not turn up your nose at those that aren't quite all you want. Once you have a couple hundred ears from a hundred plants you can get fussy and start eliminating the yellow.

The mother plant to your special ear was likely to have been homozygous for red pericarp. This means that whatever the pollen parent, every kernel is likely at least heterozygous for pericarp red. But unless there was a lot of pericarp red in the field near that spacial ear-plant, most or all kernels will likely be heterozygous, not homozygous for pericarp red. This means that about half the kernels should give you some shade of red pericarp. Most will be some shade of pink or red. You may not get any deep red at all. Don't be discouraged. When you run the frequency of the gene for the red pericarp up in the population, then you will get lots more deep red ears.

Initially I would keep every ear that is pink/red in any shade as well as all those that are white. You will need the white (clear pericarp, no aleurone color) to help you get rid of aleurone colors. And my guess is that you will find that homozygous deep red makes for lower yield and smaller ears, so you can get more vigor with a variety that retains some clear pericarp, and that gives white, red/pink, and deep red ears. Just use the lighter colors for bread of pancakes and parch the darker ones.