[NAFEX] developing hardy trees
marillen at earthlink.net
Sun Oct 25 06:28:04 EDT 2009
243 crosses? The real answer is that it depends. I'm assuming that all the 9 genes are unlinked and there is no epistasis. Even so, to do the calculation one would need additional information such as whether the favorable allele is dominant or recessive (let's not mention semi-dominant or epigenetic effects to keep things simple). Also, how are the alleles distributed between the parents? Can all the favorable alleles be found in two parents or are they distributed across 9? If the favorable allele is dominant, then we also need to know whether it exists in the candidate parent in the homozygous or heterozygous state. (If the favorable allele is recessive, then it must be homozygous). Also, keep in mind that many crosses are made just to answer these questions. So, in the end- you are right, Jerry, it can take a >lot< of crosses to combine many favorable alleles into a single progeny by conventional breeding.
Theoretically, it would be much faster to use a transgenic approach. However, the main limitation with that approach is one has to know beforehand >exactly< which alleles contribute to the trait and whether they are acting through a gain-of-function or loss-of-function on a molecular basis (though these terms generally equate with the genetic terms of dominant and recessive, respectively). It can take significant research efforts to answer those questions. So, in some cases, transgenic approaches can take longer than conventional breeding to achieve the desired phenotype.
>From: Jwlehman at aol.com
>Sent: Oct 25, 2009 12:59 AM
>To: nafex at lists.ibiblio.org
>Subject: Re: [NAFEX] developing hardy trees
>In a message dated 10/23/2009 11:07:46 AM Central Daylight Time,
>cookfrenchlick at yahoo.com writes:
>> I'm under the impression that trying to develop a plant that is at least
>> cold hardy to one more zone,in a backyard venture is like hitting the
>> Lotto. I have read that it takes a planting of several hundred seedlings and
>> then you may not get fruit quality
>You are correct. It has been my meager experience that when breeding it
>seems that the worst characteristics come out. But breeding is a numbers game
>and the breeder must be persistent.
>Lon can correct me if I'm far off. But if you are breeding to bring three
>characteristics together that is controlled by three genes each,
>mathematically you would need to make 243 crosses to recombine the best genes in one
>progeny. But in practice it could be much larger. Have you ever seen Roger
>Way's picture of 100 apples variations from 100 seedlings of the same parents?
> Here it is.
>Now make the cross to maintain quality and improve cold hardiness. The
>required number raises very fast. I believe if hardness were better in 1 in a
>hundred to get both together would be 100 X 100 or 10,000. And then the
>improvement would likely not be enough to increase hardiness by one whole zone.
>Yes, your chances with Lotto might be better.
>Sticking my neck out,
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