Hi all,
This seems like a good spot to give a basic explanation of ploidy to those who are new to the concept. For those of you who are familiar with all of this you can just ignore me, but it seems that we have a few new people on this forum who are finding it rather heavy going. LOL! In the original species Hippeastrums, it is most common for every cell to contain 22 pairs of chromosomes. In each pair it is normal for only one of the pair to be active ie working. The active chromosome is described as dominant and the inactive chromosome is described as recessive. Without getting too technical, the production of pollen and ovules splits these pairs so that each pollen grain and ovule contain one member of each pair, ie 22 single chromosomes. This is called the haploid number or n. In Hippeastrums we say then that n=22. When the pollen and ovule fuse to form the seed the 22 pairs of chromosomes are recreated in the offspring, but since the divisions in each pair are random in the first place genetic mixing occurs and the offspring are unlikely to be identical to their parents, even if the plant is self pollinated. Some combinations will result in different active chromosomes in the offspring - the classic example of this is two brown eyed parents who produce a blue eyed child because each of them carried one recessive blue eyed gene and the child ended up with two blue eyed genes. Anyway, biologists call all such organisms DIPLOID and this is the basic state of most living creatures capable of sexual reproduction.
However, sometimes, things go wrong during the production of the sex cells and they end up with double the number of chromosomes that they should have. In this case every pollen grain and ovule will have 2n chromosomes, that is two copies of each chromosome from each parent. A hippeastrum seed in which this happens will end up with 44 pairs of chromosomes, not 22 and this is called TETRAPLOIDY from the Latin tetra meaning four, because these plants now possess four time the haploid number of chromosomes rather than the original two sets. SO, what does this mean for the plant? Lets say that on Chromosome number 1 there are genes which control the speed of growth and size of the flower. The original diploid plant has one active set of these genes. They switch on and control the flower growth to a certain size. A tetraploid mutant of this plant has two active copies of the same genes so the plant gets treated to twice as much of everything: two times the amounts of plant hormones, receptors, growth factors; the lot.
Not surprisingly this tends to result in plants which are bigger and sturdier than the original diploid stock. Another side effect is the chances for more variation in any further generations. Not only does our tetraploid plant have two active copies of each chromosome, there is no reason for the two copies to be identical to each other, suddenly, instead of an either/or this gene/that gene situation you could have a trait which is off, half on, or full on depending on just which random combination the new plants have inherited. The tetraploid plants are also almost always extremely fertile in both the pollen and ovules. This is true, of course of the original diploid wild stock as well, but think what happens when you try to cross diploid with tetraploid - you end up with half a set of chromosomes which have nothing to pair up with! This leads to the following types of results - failure to produce seed, failure of seed to germinate correctly or the production of progeny which are themselves sterile, so you have a dead end, genetically speaking. As horticulturalists that doesn't bother us so much though, because we can usually fall back on vegetative propagation, should we actually produce something attractive from such a crossing, it is just that the results of getting any such offspring are low to begin with. Any plants which do result from such a combination of n + 2n chromosomes are called TRIPLOID and, though they are rare, there are a number of important triploid plants in cultivation, such as seedless watermelons and plantation bananas.
Horticultural practice has, over the years, discovered ways to artificially induce tetraploidy and other higher levels of polyploidy and tetraploid hippeastrums, daylilies and other such plants have made a significant impact on our garden landscapes since these techniques were discovered. I hope you find this information useful and here are links to a couple of pages you might like to look at if you want to study this further.
Plant Hybridisation: http://waynesword.palomar.edu/hybrids1.htm#polyploid
Hippeastrum Speadsheet: http://209.85.141.104/search?q=cache:JX8k8fw498sJ:www.botany.hawaii.edu/faculty/daehler/wra/full/Hippeastrum%2520puniceum%2520KHC.xls+hippeastrum+n%3D&hl=en&ct=clnk&cd=7&gl=au
The second one is a bit technical, but for anyone interested in producing their own hybrids there are some interesting nuggets of information buried in the spreadsheet cells
Ciao for now, KK.
