what does 3N or 4N mean in Phrag. names.

[mattbrown]

Over the last decade, it has become apparent that polyploid genomes are not always a simple sum of their constituent genomes, but products of dynamic genetic and epigenetic changes that occur upon, or shortly after, polyploid formation. Epigenetic changes, which involve alterations of gene expression without a change in DNA sequence, are particularly intriguing because they play essential roles in plant development and plant defense against viruses and transposons. In nascent polyploids, observed epigenetic phenomena include nucleolar dominance, changes in DNA methylation and chromatin structure, triggering silencing or activation of genes and (retro)transposons, and novel phenotypes (reviewed in Matzke et al., 1999; Comai, 2000; Wendel, 2000; Liu and Wendel, 2002, 2003; Osborn et al. 2003).

full article here.
http://polyploid.agronomy.wisc.edu/o...vanced-05.html

[mattbrown]

not cost effective immediately but in 5 or 10 years who knows.

[mattbrown]

Abstract
Annual Review of Ecology and Systematics
Vol. 29: 467-501 (Volume publication date November 1998)
(doi:10.1146/annurev.ecolsys.29.1.467)
<!-- End title of page and review --> <!-- Start full text content --> <!-- abstract content -->PATHWAYS, MECHANISMS, AND RATES OF POLYPLOID FORMATION IN FLOWERING PLANTS

<nobr>Justin Ramsey and </nobr>*<wbr><nobr>Douglas W. Schemske</nobr>*<wbr>Department of Botany, University of Washington, Seattle, Washington 98195-5325; e-mail: jramsey@u.washington.edu ; schem@u.washington.edu






Abstract Polyploidy is widely acknowledged as a major mechanism of adaptation and speciation in plants. The stages in polyploid evolution include frequent fertility bottlenecks and infrequent events such as gametic nonreduction and interspecific hybridization, yet little is known about how these and other factors influence overall rates of polyploid formation. Here we review the literature regarding polyploid origins, and quantify parameter values for each of the steps involved in the principal pathways. In contrast to the common claim that triploids are sterile, our results indicate that the triploid bridge pathway can contribute significantly to autopolyploid formation regardless of the mating system, and to allopolyploid formation in outcrossing taxa. We estimate that the total rate of autotetraploid formation is of the same order as the genic mutation rate (10⁵), and that a high frequency of interspecific hybridization (0.2% for selfing taxa, 2.7% for outcrossing taxa) is required for the rate of tetraploid formation via allopolyploidy to equal that by autopolyploidy. We conclude that the rate of autopolyploid formation may often be higher than the rate of allopolyploid formation. Further progress toward understanding polyploid origins requires studies in natural populations that quantify: (a) the frequency of unreduced gametes, (b) the effectiveness of triploid bridge pathways, and (c) the rates of interspecific hybridization.


the rest here but it costs$
http://arjournals.annualreviews.org/...olsys.29.1.467

[mattbrown]

<table border="0" cellpadding="6" cellspacing="2" width="90%"> <tbody><tr><td align="right" bgcolor="peachpuff" valign="top" width="5%">
</td> <td align="left" valign="top">Triploid Bridge and Role of Parthenogenesis in the Evolution of Autopolyploidy</td></tr></tbody> </table> Atsushi Yamauchi, Azusa Hosokawa, Hiromi Nagata, and Miyuki Shimoda
http://www.journals.uchicago.edu/AN/.../30129.web.pdf

[LJA]

Yah, but there's the rub. What they're calling a "significant contribution" may well be significant on an evolutionary scale, but it's nowhere near the rate needed by, say, orchid hybridizers to reliably produce crops from a triploid parent. Of course, that isn't their aim; they're trying to understand and explain a mechanism by which polyploidy has occured in the wild. Once those pathways are understood well enough to be artificially and inexpensively reproducible...

[mattbrown]

well there is some work being done on a microsurgical technique for enucleation of multipronuclear human/other mamalian zygotes. First attempts to remove a single pronucleusmicrosurgically from human triploid zygotes, in order to correctthem to diploid status, was reported in 1988. (i forget by whom...)
there is hope.

[mattbrown]

Meiosis may be difficult for triploid cells because of the odd number of homologous chromosomes, triploid individuals are often characterized by low fertility. Inspite of such difficulty, triploid individuals often produce normal gametes.
Ramsey & Schemske(98) pointed out that in some plant species, a large fraction of gametes produced by autotriploids are nonfunctional aneuploids, although a few are haploid, diploid, or triploid. some studies using artifically induced aototriploids have also shown that triploids possibly produce haploid and diplgametesetes. Gupta & Gill (84), Kuspira et al. (86), Kumar et al. (87), Ramsey & Schemske(98).
in this model it is considered that triploid individuals produce haploid, diploid, and triploid gametes with certain probabilities.
[---Ramsey & Schemske(98) reviewed25 studies of pollen production in triploid plants, including both hybrid and non-hybrid triploids. according to this review, the average frequencies of haploid, diploid, and triploid gametes produced by triploids were 3%, 2%(n=25), and 5.2%(n=9), respectively. the remaining gametes were aneuploid, being a major fraction of the pollen produced. it is assumed that a triploid individual has the gamete production ability as a diploid, although only 10.2% (3%+2%+5.2%) of the gametes produced are normal euploid(haploid, diploid, and triploid).---]


diploid= 1x
triploid= 1x,2x,3x
tetraploid=2x

(1x) diploid X (1x) diploid=2x
(1x) triploid X (1x) diploid=2x
(1x) triploid X (1x) triploid=2x
(2x) triploid X (1x) diploid=3x
(2x) triploid X (1x) triploid=3x
(2x) triploid X (2X) triploid=4x
(3x) triploid X (1x) diploid=4x
(3x) triploid X (1x) triploid=4x
(3x) triploid X (2X) triploid={5x}
(3x) triploid X (3X) triploid={6x}
(2x) tetraploid X (1x) diploid=3x
(2x) tetraploid X (1x) triploid=3x
(2x) tetraploid X (2X) triploid=4x
(2x) tetraploid X (3X) triploid={5x}
(2x) tetraploid X (2x) tetraploid=4x

numbers represent ploidy of zygotes and gametes
{_} represents offspring that are considered unviable due to their high ploidy levels. Each gamete of diploid and tetraploid individuals involves half the number of chromosomes as somatic cells. in contrast gametes of triploids involve various sets of chromosomes because triploid individuals can't undergo meosis normally owing to the odd number of homologous chromosomes.

[mattbrown]

Yes, they are trying to understand and explain a mechanism by which polyploidy has occured in the wild but once it is understood it may break down the triploid sterility bottleneck in orchid breeding.

Yah, but there's the rub. What they're calling a "significant contribution" may well be significant on an evolutionary scale, but it's nowhere near the rate needed by, say, orchid hybridizers to reliably produce crops from a triploid parent. Of course, that isn't their aim; they're trying to understand and explain a mechanism by which polyploidy has occured in the wild. Once those pathways are understood well enough to be artificially and inexpensively reproducible...

OK, in nature, think about an isolated plant population. ok some of them are diploid some are tetraploid. what prompted the polyploid segment of the population to do so. perhaps a diploid failed to properly divide durring meiosis creating a triploid. now we have diploids, tetraploids, and triploids in our population. now lets say that through selfing/or parthenogenisis a triploid produces a 2n gamete. now we are in business.

At the initiation of polyploidization, tetraploids tend to rapidly decrease because their offspring are almost always triploid due to mating with dominant dipliod individuals. however if the triploid cytotype effectively by parthenogeneisis, they gradually increase in frequency and coexist with the diploid individuals (but without genetic interactions), finally taking over the population. when the diploid cytotype is almost excluded, the tetraploid can invade and increase in the population.

If a tetraploid population becomes established even when the "triploid bridge" works less efectively , this process is mainly infuenced by direct competition between triploids and tetraploids.

[mattbrown]

So, to make sure I'm getting this triploid bridge: a diploid parent fails to divide meiotically and contributes its full 2N, which when combined with a normally dividing individual contributing 1N, yields a 3N zygote. This triploid then also needs to fail to divide properly, contributes 3N instead of 1.5N, and when combined with a normal 1N, yields a tetraploid, 4N individual.

tripliod bridge
ok
diploid devides normally =2n
triploid can contribute= 1n(3%), 2n(2%), or 3n(5.2%)... (frequency of occurence)
ok ...diploid and haploid are represented as 1x because they both contribute one set of chromesomes durring meiosis. true triploids are represented as 3x. tetraploids are represented as 2x.

diploid@1x + triploid@1x = 2x=triploid bridged
diploid@1x + triploid@2x = 3x=triploid block
diploid@1x + triploid@3x = 4x=triploid bridged

[LJA]

Thanks, Matt. Very good and detailed explanations. Maybe one day I'll be in a position to do some experimentation--I always enjoy knowing the "why" of things. Much appreciated!