Genetics Question

If you cross breed two F6, stable varieties with desirable characteristics, can genetically induced undesirable traits present in the parentage of the F6 varieties reappear in the resulting F1 variety?

Ted

[Fusion_power]

If the trait is recessive, yes. More important, there are several traits such as color that are controlled by multiple genes. So you could cross a green when ripe variety with a yellow variety and the offspring would give about 50% red tomatoes.

DarJones

[maf]

Originally Posted by tedln

If you cross breed two F6, stable varieties with desirable characteristics, can genetically induced undesirable traits present in the parentage of the F6 varieties reappear in the resulting F1 variety?

Ted

You are talking about traits that seem to have disappeared in the F6's?

I would say no, they will not reappear in the F1. As DarJones says, there is a possibility that undesirable recessive traits are lurking unseen in the F6 lines, but these would usually only show up in the F2 and beyond, not in the F1. (The exception would be if both F6 parents had a hidden copy of the exact same recessive gene and they happened to combine as a pair in 25% of the F1 seeds.)

The F6's would still not be 100% stable; if you repeated the experiment with F9 or F10 lines the chances of any hidden undesirable traits would have diminished almost to zero.

Originally Posted by Fusion_power

you could cross a green when ripe variety with a yellow variety and the offspring would give about 50% red tomatoes.

I thought the cross of a GWR x yellow would give a yellow in the F1 and segregate for yellow and GWR in the F2 and subsequent generations? Am I misunderstanding something about the example given here?

[Fusion_power]

I thought the cross of a GWR x yellow would give a yellow in the F1 and segregate for yellow and GWR in the F2 and subsequent generations? Am I misunderstanding something about the example given here?

The green when ripe gene is a deletion in a key gene in the chain that leads to lycopene. The yellow gene is another change in the same sequence but further up the line. When you cross the two, you get some offspring that bypass GWR because of the coding that came from the yellow variety and you get some offspring that bypass the yellow gene because of coding on the GWR variety. The net effect is to turn back on Lycopene. The number of plants that express the trait could be from from 3:16 to 8:16 depending on which version of the yellow gene is involved. As an aside, the red color expressed is sometimes an almost glowing bright cherry red, probably from an interaction between the variants.

Note that in the F1, the color could range from Salmon to Pink to Red. In the F2, you would get the full range of expression from GWR to salmon to yellow to red to glowing red. I have some F2 seed from Cherokee Green X a yellow variety that expresses these colors very nicely.

DarJones

[maf]

Ah, ok, I was thinking of GWR in terms of a tomato with the gf (green flesh) gene, which retards the breakdown of chlorophyl, in a yellow fleshed background. My previous example would have been a cross between a gf/gf, r/r line and an r/r line.

Which specific gene are you referring to? Gr (Green ripe)?

[goodwin]

gf is the result of a mutation, and several different insertions/deletions which lead to these mutant alleles have been identified. So it could be more complicated, I think.
Lee

[Tom Wagner]

If you cross breed two F6, stable varieties with desirable characteristics, can genetically induced undesirable traits present in the parentage of the F6 varieties reappear in the resulting F1 variety?

Ted, Tomato breeding is often a ZERO SUM GAME.

Of or relating to a situation in which a gain is offset by an equal loss:

or one trait of a tomato hybrid's gain is countered with another trait of that same tomato hybrid's loss.

The opposite of a zero-sum game is a negative-sum game, in which nothing is gained, and whatever they've lost means that those tomatoes are thrown into a neighbor's yard , never to be seen again.

That means one can take a dozen or so stable (F-6 or better) varieties....cross 'em up in several dozen crosses....and even though all of the parents were decent enough...the combining ability of these hybrids can be all over the map..good, average or even poor. The key term is COMBINING ABILITY...and breeders will always tell you that making hybrids..... is hoping to have all of the benefits of the cross and none of the negatives.

I have found great success in crossing varieties (clones) that have minor and major defects by themselves, but in the hybrid produce splendid tomatoes with few if any defects.

Twenty years ago hybrids such as Sunjay and Merced were all the rage in California for the mature green pick. But each had some flaws. By selfing Sunjay and Merced to the F-5 level or so I accumulated a few strains that seemingly were worse than the respective hybrids. Sunjay F-1 was a great tomato for it's time....high yields, nematode resistant, big vines that protected the fruits from the hot California sun. But it tended to be a bit too late. Conversely, Merced was early, very red in color, easy to pick, but was not nematode resistant. I selfed out a strain of Sunjay to be homozygous for nematode resistance but that carried a genetic drag of misshapened fruit..etc, jointless stem fruits, super large vines and very late. Merced lines were selfed down to vines that were too compact and small, fruits subject to sun scaldand of course...susceptible to nematodes.

Making a hybrid of these two misfits was surprisingly good. The hybrid was high yielding with none of the genetic drag of nematode resistance but were still resistant enough for California at that time, jointed pedicels that made the fruit detach at the joint or at the stem scar, had sufficient cover against the hot sun, and ripened to a full red color. The combining ability of these two misfits was outstanding. The F-2 generation was hugely divergent and few of the recombinations were met with much favor.


Have I bred up heirloom type tomatoes that are full of undesirable characteristics? You bet! I wont release them on my website because they are good for only one thing.....making great hybrids!

Tom,

Since my knowledge of genetics is limited, could an analogy of a genome be an electrical circuit or micro electronic circuit comprised of an infinite number of relays or transistors?

Each relay or transistor would only have potential on and/or off positions, but the condition of many could be dictated by the condition of more than one. A circuit could be easily mapped and totally predictable and repeatable.

Can the same be said of organic genetics with the various resulting traits being able to skip generations but with the ability to reappear or disappear depending on generational and/or parental input?

A mutation would essentially be comparable to a malfunction in the circuit with good or bad results.

Ted

[goodwin]

You could model this information as a series of logic gates, but there is perhaps a better analogy.
Many of these mutations are frame shifts, and each segment codes for something like building a protein.
In nature there are 4 letters in the genetic alphabet and all words (codons) are three letters long. Say you wanted to decode the sequence AFATCATATETHERAT...
If you were told the first 'A' signals the beginning and it is chopped up into codons you would get
A FAT CAT ATE THE RAT. However if a deletion occurs which knocks out the 'C' you get
A FAT ATA TET HER AT.. And that sends a completely different message to the cell.
Anyway, that is sort of a simplified version of what is going on.

[Fusion_power]

Mutations are not uncommon. In fact, it is estimated that every tomato plant grown from seed has at least 2 mutations that were not present in the parent. Fortunately, things don't get too cluttered up because there is a huge amount of junk DNA in each cell. Most of the mutations occur in places where they are harmless.

Think of a given stable open pollinated line of tomatoes as a set of genes and another stable open pollinated line as another set of genes. At least 99% of the genes are going to be identical. But that 1% contains a huge amount of diversity. The 1% represents all of the color variations, all of the fruit shape variations, and most of the rest of the traits we are familiar with. I've read that the genes for fruit shape and color are estimated to be 10 or 12 at most.

Note that there are numerous variants of gf that all give the same result. Some are deletions, some are insertions, some are transpositions. The impact is to disable the gene that normally causes chlorophyll to be converted through a sequence of steps into lycopene. Please note that in most backgrounds I have grown gf is the only significant mutation in that genetic sequence therefore if you cross with just about any other variety except another green when ripe, you are going to re-enable lycopene. As noted by Maf above, if gf were moved into a background that included yellow flesh, then the above example I gave would no longer hold true. The cross of (gf,r) X ( r) would always result in a yellow flesh tomato. This is simplistic because there are multiple variants that result in yellow fruit. As an aside, the "y" gene is the gene for epidermis color. The reason "r" is for yellow is because "r" is the recessive for the wild type red color.

http://tgrc.ucdavis.edu/Data/Acc/GenDetail.aspx?Gene=gf
http://tgrc.ucdavis.edu/Data/Acc/GenDetail.aspx?Gene=r

DarJones