the triploids (3X) and pentaploids (5X) survive in nature by vegetative propagation. rarely do they produce viable seeds. The cultivated Banana is a triploid propagated by the rhizome while the wild banana which is a diploid sets seeds.

You will get all these answers in any elementary book on Genetics like Gardner's Principles of Genetics, or Russel- Genetics. oif you need further information please do let me know. will send you some information from my book for BSc students.

Thanks for your answer. But my question is about their meiosis.

Okay. Meiosis obviously will be irregular. In triploids you may get a univalent and a bivalent for the three homologous chromosomes or a trivalent ot 3 univalents each. hence at anaphase I you may get two chromosomes migarating to one pole and one to the other and varying levels of aneuploidy. its all given in the books I have suggested.

This is from what I give in the class. Sorry unable to load the diagrams.

Cytologically the triploid cells have three sets of chromosomes. Triploids are characteristically sterile, the problem being pairing at meiosis. Pairing of chromosomes at Prophase I of meiosis can take place only between two chromosomes to form bivalents, but one of the three homologues of a triploid can pair with one partner along a part of its length and with another along the remainder, giving rise to an association of three chromosomes i.e. trivalent formation (Fig)

Or there may be the formation of a bivalent and one chromosome may remain unassociated as a univalent .

At metaphase I the trivalents and bivalents lie haphazardly on the equatorial plate and the univalents lie outside the spindle. At anaphase I if all the single chromosomes of the entire set migrate to one pole and simultaneously the other two chromosomes pass to the opposite pole(Fig.), then the gametes formed will be haploid and diploid.

This probability however is very low. All other possibilities will give gametes with chromosome numbers intermediate between the haploid and diploid number (Fig. 3.10), i.e. aneuploid genomes. As a result triploids produce a range of aneuploid offsprings.

However the addition of one or more extra chromosomes is nearly always deleterious because the proportion of genes in those extra chromosomes is altered. The deleterious effect can be expressed at the level of gametes making them non functional, or at the level of the zygote, resulting in lethality, sterility or lowered fitness.

The triploids hence are vegetatively propagated. The cultivated bananas are triploids with 11chromosomes in each set (3x=33). The most obvious expression of the sterility in banana is that there are no seeds in the fruits that we eat.

thanks for a nice answer. one more question. How we can determine their nature whether allo- or autopolyploid

Our experience with triploid deciduous azaleas indicates that those that are seed fertile display irregular meiosis that is distributed around 1.5x. Crosses involving 3x X 4x produce offspring that are near 3x, between 3x and 4x, near 4x, and near 5x where the majority are aneuploids between 3x and 4x. The distribution of the offspring depends on both parents.

The triploid deciduous azalea we are working with are crosses between closely related diploid and tetraploid species so are almost certainly allotriploids. However the flow cytometry scores for the diploid and tetraploids are in a ratio almost exactly 1 to 2. Both the diploid and tetraploid species show "normal" meiosis when doing crosses within each species. Neither the diploid speceis nor tetraploid species is self fertile.

One seedling of a deciduous azalea cross of 3x X 4x produced seed when crossed with pollen from a 4x.

The seedling of 3x X 4x had a flow cytometry score in the pentaploid range so this cross of (3x X 4x) X 4x was in effect 5x X 4x.

We also produced seed from the following deciduous azalea crosses:

6x X 6x

4x X 6x

6x X 4x

These 6x parents where produced from 4x X 8x.

The 8x was a chemically induced from a tetraploid parent.

The 4x was tetraploid deciduous azaleas species.

The 3x was produced from 2x X 4x.