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

LJA · #21 03-04-2005, 06:10 PM

Have one question though, now that I look this over again. If, not counting triploid block, frequency of occurence adds only to 8.2%, what happens the rest of the time? Does meiosis just never occur, or are the chromosomes just so scrambled (nonfunctional aneuploids) that they can never hope to combine with those of the other gamete?

LJA · #22 03-04-2005, 07:01 PM

Maybe more importantly (in terms of a practical application), does the research show what chemical factors (possibly environmental "signals") contribute to triploid "sterility?" Or, the reverse: what factors inhibit a triploid from contributing 3n or 1n, all of the time? What makes the percentages of successful contribution so low?

mattbrown · #23 03-05-2005, 10:26 AM

good question!
it is still computed as 10.2% this is an average of viable gametes produced by a triploid. the model given was one possible scenario.

Quote:

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

it may not always be true.
if the diploid fails to divide it is bridged(=2n). if the triploid fails to divide it is also bridged(=2n). if it self's w/ another triploid gamete@2x it is bridged(=4n). if it reproduces parthogenetically the same out come of 4n can be expected.

Quote:

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

Quote:

Does meiosis just never occur, or are the chromosomes just so scrambled (nonfunctional aneuploids) that they can never hope to combine with those of the other gamete?

yes. 89.8% of the the triploid gametes produced are scrambled aneuploids.
it is not believed that they are capable of interacting w/ other gametes.

Quote:

Originally Posted by lja

Have one question though, now that I look this over again. If, not counting triploid block, frequency of occurence adds only to 8.2%, what happens the rest of the time? Does meiosis just never occur, or are the chromosomes just so scrambled (nonfunctional aneuploids) that they can never hope to combine with those of the other gamete?

mattbrown · #24 03-05-2005, 10:50 AM

Quote:

Originally Posted by lja

Maybe more importantly (in terms of a practical application), does the research show what chemical factors (possibly environmental "signals") contribute to triploid "sterility?" Or, the reverse: what factors inhibit a triploid from contributing 3n or 1n, all of the time? What makes the percentages of successful contribution so low?

the first part of your question:

Quote:

Maybe more importantly (in terms of a practical application), does the research show what chemical factors (possibly environmental "signals") contribute to triploid "sterility?

ok,
there are many factors contributing to triploid diminished reproductive fitness ("sterility").
1.) supposing aneuploid gametes as being completely nonfunctional, the fertility of triploids in sexual reproduction can be taken as 10.2%.
2.) endosperm collapse of triploid seeds.
these are the main hurdles.
--in order for a sexually reproducing triploid to succeed, they must be among functional gametes.--

part 2:

Quote:

what factors inhibit a triploid from contributing 3n or 1n, all of the time

i don't know. but 2n is also a valuable contribution(as stated below).

hope this helps if anyone has more questions just post them here.

LJA · #25 03-05-2005, 09:52 PM

Okay. So we have a good model with some reasonable percentages regarding triploids producing fertile gametes. Obviously these are not random events or the percentages would be much different. So do we know what kind of chemistry is going on? There has GOT to be some chemical trigger that induces a triploid to produce viable gametes in the face of 90% sterility. What causes that? Why only 10% of the time? What environmental factors induce a chemical change that produces fertility? Is there any research underway that addresses this? Any grad students out there who want to take this on and get rich off the findings?

mattbrown · #26 03-06-2005, 09:44 AM

Parthenocarpy restores fruitfulness in sterile triploid (3x) tomatoes artificially obtained by crossing 4x x 2x somaclones

Authors: HABASHY A.A.; TESTA G.; ROH P.; MOSCONI R.; CACCIA A.; MAZZUCATO E.; SANTANGELO G.P.

Source: The Journal of Horticultural Science and Biotechnology, March 2004, vol. 79, no. 2, pp. 322-328(7)

Publisher: Journal of Horticultural Science and Biotechnology Trustees

Abstract:

Quote:

To breed fruitful triploid tomatoes, diploid (2x) and tetraploid (4x) plants were regenerated from hypocotyl explants, using two pairs of near-isogenic lines differing respectively for the parthenocarpic fruit and parthenocarpic fruit-2 mutations. From 626 regenerated shoots, 53 were tetraploid. In the 4x plants, the mean number of fruits was lower than in the 2x class for all the genotypes, but in the two parthenocarpic lines it was higher than in the respective wild-types at the same ploidy level. Compared with 2x, the mean weight of 4x fruits was lower in wild-type and higher in parthenocarpic lines. Out of four cross combinations between tetraploid and diploid plants (within two parthenocarpic and two corresponding wild-type lines), only two yielded seeds (the parthenocarpic fruit line and its near-isogenic wildtype). Triploids were vegetatively propagated and evaluated in a field trial. Whereas wild-type triploids were completely sterile, the 3x parthenocarpic fruit plants had a fruit set that was not statistically different from that observed in 2x individuals. Mean fruit weight in 3x parthenocarpic plants was also higher than in 2x and comparable with 4x plants.Yield estimates in such triploids were not statistically different from those recorded in diploids, both wild-type and parthenocarpic. Triploid fruits had a soluble solids value higher than 2x fruits. The total seedlessness and the increased dry-matter content appeared traits peculiar to triploid parthenocarpic fruits. Therefore, triploids may deserve interest in breeding fresh market and processing tomatoes, providing that their commercial multiplication is ensured by micropropagation.

it might be easier to develop a micropropigation technique for reproducing 3n orchids(paphs & phrags).
i mean if we can clone a whole sheep...

mattbrown · #27 03-06-2005, 09:49 AM

PATHWAYS, MECHANISMS, AND RATES OF POLYPLOID FORMATION IN FLOWERING PLANTS Justin Ramsey and *Douglas W. Schemske*Department of Botany, University of Washington, Seattle, Washington 98195-5325; e-mail: jramsey@u.washington.edu ; schem@u.washington.edu

Quote:

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

5), 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.

Quote:

We estimate that the total rate of autotetraploid formation is of the same order as the genic mutation rate (10

5)

(10

5)= .000001 or 1 in 1,000,000

--not really relevant to louis's question but an interesting figure.--

LJA · #28 03-07-2005, 04:47 PM

LOL! Yes, but still better odds than playing any multi-million State Lotto!

Thanks, Matt. In a few years' time, we may very well see Maud 'The Queen' parents which aren't a bunch of nonsense.....