somatic mutation - Page 2

Heritage · August 14, 2013

Scott, you are correct about the possibility of the pink fruit not being stable. I had my previous red-to-yellow example on the brain when I said the pink fruit would produce all stable/pink fruit. In the case of a red-to-yellow somatic mutation all of the yellow fruit will produce stable yellow-fruited plants because you end up with a homozygous recessive for both yellow flesh and clear epi (yyrr).In the case of white-to-pink you would have to do a normal grow out to eliminate any possibility of heterozygous dominants (Rr) showing up in future generations. I don't think the plant from bejustice is a somatic mutation but, assuming it was: the pink fruit from such a somatic mutation is either yyRr or yyRR - most likely yyRr. Assuming self-pollination, expect a grow out of the pink fruit to present a genotype of 1/4 yyRR, 1/2 yyRr, and 1/4 yyrr, or a phenotype of 3/4 pink and 1/4 white fruit.

In plants, cells destined to become gametes do arise from somatic tissues. Plants, unlike animals, do not have a germ line. The fact that meristem organization is very flexible (contain a large number of undifferentiated cells) can allow accumulation of somatic mutations; most of the somatic mutations are not immediately life-threatening. There is genetic evidence that the developmental program of somatic and zygotic embryos is indistinguishable. The article Chris referenced above addresses this concept.

Anyway, in this particular case, with the weakened plant showing up along with the change in fruit color, it sounds like the mutation may have affected more than one gene and "messed up a whole chunk of the chromosome". If the initial grow out of, say 50(?), plants from the pink-fruited seed produces any white-fruited plants then I think the student would be better served to start from scratch and cross the white cherry with a robust pink cherry, then select for the desired traits. In this case it should only require one additional generation of grow outs and would also provide the student with more of an education.

Scott, our bottom line advice to bejustice is the same

- the seeds from the pink fruit have to be grown out and evaluated - stability can not be assumed.

Steve

frogsleap farm · August 14, 2013

In seed propagated plants a mutation-related phenotype is only expressed when it is heritable – passed on from one sexual generation to the next. Most of these heritable mutations arise in meiosis during the generation of male (pollen) or female (ovule) gametes – often referred to as germ cells. There are numerous mutations arising from mitosis in somatic cells which are not heritable, unless a flower bud arises directly from a “sport” tracing to such somatic mutation. Although these are rare, as many have pointed out here, they do happen.
If there is a mutation-related phenotype in fruit tracing to a somatic mutation, the mutation is by definition a dominant mutation, i.e. a single copy of a mutant allele is sufficient to express the mutant phenotype. It is exceedingly rare to get simultaneous and identical mutations on both chromosomes. Dominant mutations are due to a mutant hyperactive allele masking the wild type allele – typically, but not always, gain of function mutants. As pointed out in this thread, these will segregate 3:1 in the following generation. A recessive mutation almost always results in a loss of function phenotype, and will not be expressed directly in fruit tracing to a somatic mutation, or in the first generation after a meiotic mutation. Two copies of a recessive mutant allele (homozygous state) are required for expression of the mutant phenotype. The comment here that mutations sometimes “skip a generation” is due to fact that a mutant homozygous recessive phenotype is only possible after a sexual generation of recombination.

Heritage · August 15, 2013

Quote:

Originally Posted by frogsleap farm

It is exceedingly rare to get simultaneous and identical mutations on both chromosomes. Dominant mutations are due to a mutant hyperactive allele masking the wild type allele

Thanks, another good point I missed. So, a red-to-yellow fruit mutation would require (except in extremely lucky cases) that the original red was heterozygous (Rr) for fruit color and not a stable specimen to begin with.

bejustice · March 15, 2017

Grow outs were all pink. It is really a peachy pink with clear skin. We have grown over 1000 plants over the last two seasons, all pink. It came from a white cherry from Johnnies Seeds. It was a sickly plant, but it's first and second generation have done well, better than white cherry. I want to cross it with it this season.

August 14, 2013	#16
Heritage Tomatovillian™ Join Date: Nov 2010 Location: San Diego Posts: 1,255	Scott, you are correct about the possibility of the pink fruit not being stable. I had my previous red-to-yellow example on the brain when I said the pink fruit would produce all stable/pink fruit. In the case of a red-to-yellow somatic mutation all of the yellow fruit will produce stable yellow-fruited plants because you end up with a homozygous recessive for both yellow flesh and clear epi (yyrr).In the case of white-to-pink you would have to do a normal grow out to eliminate any possibility of heterozygous dominants (Rr) showing up in future generations. I don't think the plant from bejustice is a somatic mutation but, assuming it was: the pink fruit from such a somatic mutation is either yyRr or yyRR - most likely yyRr. Assuming self-pollination, expect a grow out of the pink fruit to present a genotype of 1/4 yyRR, 1/2 yyRr, and 1/4 yyrr, or a phenotype of 3/4 pink and 1/4 white fruit. In plants, cells destined to become gametes do arise from somatic tissues. Plants, unlike animals, do not have a germ line. The fact that meristem organization is very flexible (contain a large number of undifferentiated cells) can allow accumulation of somatic mutations; most of the somatic mutations are not immediately life-threatening. There is genetic evidence that the developmental program of somatic and zygotic embryos is indistinguishable. The article Chris referenced above addresses this concept. Anyway, in this particular case, with the weakened plant showing up along with the change in fruit color, it sounds like the mutation may have affected more than one gene and "messed up a whole chunk of the chromosome". If the initial grow out of, say 50(?), plants from the pink-fruited seed produces any white-fruited plants then I think the student would be better served to start from scratch and cross the white cherry with a robust pink cherry, then select for the desired traits. In this case it should only require one additional generation of grow outs and would also provide the student with more of an education. Scott, our bottom line advice to bejustice is the same - the seeds from the pink fruit have to be grown out and evaluated - stability can not be assumed. Steve Last edited by Heritage; August 14, 2013 at 08:21 PM.

August 14, 2013	#17
frogsleap farm Tomatovillian™ Join Date: Nov 2008 Location: Minnesota Posts: 568	In seed propagated plants a mutation-related phenotype is only expressed when it is heritable – passed on from one sexual generation to the next. Most of these heritable mutations arise in meiosis during the generation of male (pollen) or female (ovule) gametes – often referred to as germ cells. There are numerous mutations arising from mitosis in somatic cells which are not heritable, unless a flower bud arises directly from a “sport” tracing to such somatic mutation. Although these are rare, as many have pointed out here, they do happen. If there is a mutation-related phenotype in fruit tracing to a somatic mutation, the mutation is by definition a dominant mutation, i.e. a single copy of a mutant allele is sufficient to express the mutant phenotype. It is exceedingly rare to get simultaneous and identical mutations on both chromosomes. Dominant mutations are due to a mutant hyperactive allele masking the wild type allele – typically, but not always, gain of function mutants. As pointed out in this thread, these will segregate 3:1 in the following generation. A recessive mutation almost always results in a loss of function phenotype, and will not be expressed directly in fruit tracing to a somatic mutation, or in the first generation after a meiotic mutation. Two copies of a recessive mutant allele (homozygous state) are required for expression of the mutant phenotype. The comment here that mutations sometimes “skip a generation” is due to fact that a mutant homozygous recessive phenotype is only possible after a sexual generation of recombination.

March 15, 2017	#19
bejustice Tomatovillian™ Join Date: Jul 2013 Location: Timberlake, nc Posts: 50	Grow outs were all pink. It is really a peachy pink with clear skin. We have grown over 1000 plants over the last two seasons, all pink. It came from a white cherry from Johnnies Seeds. It was a sickly plant, but it's first and second generation have done well, better than white cherry. I want to cross it with it this season.