Orchid Care OrchidTalk Orchid Forum Links Nursery

Welcome to OrchidTalk Orchid Forums


The Friendliest Orchid Community on the Internet!


  •  » Learn to Repot your Orchids
  •  » Learn Orchid Care Tips and Secrets
  •  » Find the perfect Orchid for your Growing Environment
  •  » Chat with Orchid Growing Professionals

OrchidTalk - "Bringing People Together to Grow Orchids Better!"


Let us help you grow your Orchids better; Join our community today.


YES! I want to register an account for free right now!


Register or Login now to remove this advertisement.

Page 2 of 3 FirstFirst 123 LastLast
Results 11 to 20 of 28

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

Click here to increase the font size Click here to reduce the font size
  1. #11
    Join Date
    Feb 2005
    Location
    florida
    Posts
    88

    Default

    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

  2. #12
    Join Date
    Feb 2005
    Location
    florida
    Posts
    88

    Default

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

  3. #13
    Join Date
    Feb 2005
    Location
    florida
    Posts
    88

    Default

    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 (10<sup>5</sup>), 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

  4. #14
    Join Date
    Feb 2005
    Location
    florida
    Posts
    88

    Default

    <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

  5. #15
    Real Name
    Louis J. Aszod
    My Grow Area
    Greenhouse
    Favorite Orchid(s)
    Cattleya
    Join Date
    Feb 2003
    Gender
    Male
    Location
    Clarksville, Arkansas
    Posts
    3,780
    Member's Country Flag

    Default

    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...

  6. #16
    Join Date
    Feb 2005
    Location
    florida
    Posts
    88

    Default

    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 pronucleus<sup> </sup>microsurgically from human triploid zygotes, in order to correct<sup> </sup>them to diploid status, was reported in 1988. (i forget by whom...)
    there is hope.


  7. #17
    Join Date
    Feb 2005
    Location
    florida
    Posts
    88

    Default

    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.

  8. #18
    Join Date
    Feb 2005
    Location
    florida
    Posts
    88

    Default

    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.



    Quote Originally Posted by 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...
    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.

  9. #19
    Join Date
    Feb 2005
    Location
    florida
    Posts
    88

    Default

    Quote Originally Posted by lja
    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

  10. #20
    Real Name
    Louis J. Aszod
    My Grow Area
    Greenhouse
    Favorite Orchid(s)
    Cattleya
    Join Date
    Feb 2003
    Gender
    Male
    Location
    Clarksville, Arkansas
    Posts
    3,780
    Member's Country Flag

    Default

    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!

Similar Threads

  1. 2 NO NAMES IN FLOWER
    By SEASIDEJOHN in forum General Orchid Culture
    Replies: 3
    Last Post: February 3rd, 2009, 06:35 AM
  2. How to put names on photos
    By 1buzz in forum Using the Boards
    Replies: 4
    Last Post: December 9th, 2008, 07:55 PM
  3. Help with some names, awards, etc..
    By Brutal_Dreamer in forum General Orchid Culture
    Replies: 1
    Last Post: April 27th, 2008, 09:30 PM
  4. names of things
    By nabakov5 in forum General Information
    Replies: 2
    Last Post: May 30th, 2006, 10:22 PM
  5. Genus names?
    By orchidmanONCID in forum Breeding & Hybridization
    Replies: 7
    Last Post: January 1st, 2005, 06:42 PM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
OrchidTalk --An Orchid Growers Discussion Forum brought to you by River Valley Orchidworks. A World Community where orchid beginners and experts talk about orchids and share tips on their care, cultivation, and propagation.