Quote: >>I have never heard of any authenticated haploid strains of orchids in any >>genus. Can you or anyone else >point me in the direction of some paper or >>publication where they are documented?
I don't think that angiosperms can be adult and haploid, unlike bryophytes. However, the original point of the thread was whether a haploid gamete could have its chromosome number doubled to diploid status, but be a fixed homozygous adult. The answer is that it can, and that this is routinely done in agricultural plant breeding. EG :High frequency production of doubled haploid plants of Brassica napus etc Journal Plant Cell Reports Issue Volume 15, Number 9 / May, 1996 Why should anyone want to do this? Because it can fix a desirable genetic situation that would otherwise not breed true, by making the offspring plant homozygous for that gene. That is, heterozygous plants will produce progeny which mix together genes in ways which destroy the desirable configuration that you found in the parent. If the trait you value comes from two genes, then you will need of course a haploid that holds these genes. If they are located on the same chromosome, but on separate members of the pair (one gene on chromosome A, the other on B) then you will not be able to make a haploid that has both. If you are looking at the consequences of many genes, you need a haploid which just happens to have a copy of all of these in it. So this is not a magic wand. I do not know, but I assume that this has not been done in orchids. Excepting perhaps Vanilla, no orchids are used for monotypic features, like oil quality or sugar levels at harvest. Multi feature qualities, such as complex flower colouration - encounters problems, as described above. The economic scale is anyway not there, at least as it is for oilseed rape (canola, as above) and meristem or other clonal propagation does the same job, but without all of the caveats just discussed. >Please consider sharing your findings with all of us on the OGD. A simple >explanation of >the genetic terms used may be helpful. KwikiWiki: Angiosperms - plants that reproduce sexually, with flowers as their genitalia. Chromosome - bundles of genetic material, copied during cell division and "crossed over" - intermingled - during sexual reproduction. (This is called meiosis.) Most organisms with nuclei in their cells, and all plants, have many such pairs of chromosomes in each cell. Bryophytes - plants such as ferns, mosses and liverworts(?) Diploid - the normal state of most organisms. Each cell has two copies of each chromosome, one derived from each parent. (Gender-related chromosomes are slightly different in this respect, that that's irrelevant here.) Haploid - a cell or gamete containing only one set of chromosomes. These are randomly selected from amongst the pairs. If the selection is a part of the sexual process, then the two chromosomes are mixed their genetic material and re-partitioned before this happens. A haploid cell which has been produces in this way is called a 'gamete', an example being pollen. When two gametes fuse, the result achieves diploid status. That is, there are now two pairs of chromosomes in the resulting cell. The cell is not identical to either parent but rather a blend of the two; and each parent has passed down a blend of their mixed diploid status through this process. The mature organism is made from duplicate of this genetic blend, with the DNA in each cell line - epidermal cells, vessels and so forth - modified chemically so as to alter the patterns in which genes are switched on an off, so called 'epigenetic change'. Epigenetics affect whether cloning works perfectly, about which more below. Heterozygous - an organism in which the two copies of its DNA that is held in the twin sets of chromosomes is different. One set came from each parent, which were themselves different. Heterozygous organisms do not breed true, but show "hybrid vigor". Homozygous - an organism in which, by contrast, both sets of chromosomes have identical DNA. (Often used in the sense of 'homozygous for', meaning that the organism has two identical genes or sets of genes 'for' something, although the rest of it is heterozygous and mixed. Homozygous organisms do breed true, but do not show hybrid vigor. Some versions of a particular gene may be suboptimal. In heterozygous organisms, the other copy may well be "better", and mask this weakness. In homozygous organisms, this does not happen. There is a consequence of hybrid vigor. Many species orchids grow slowly when compared to hybrids. This is often because the genetic structure is optimised around managing crises such as droughts, which creates the equivalent of caution. Genetics which throws these limits to the winds can be seen as "better" by a breeder seeking fast growth and perpetual flowering. So the 'cautious' versions of these genes are weeded out, or more commonly masked with a single 'incautious' gene. Clone, clonal - an adult organism developed from a single cell or cluster of cells (a callus, see below) in which the chromosomes have never deviated from diploid status, or been mixed together by crossing over. That is, the adult that results is largely identical to the adult from which it was developed. (This is not precisely true due to what are called "epigenetic tags". These are chemical modifications to the DNA itself, which are applied during embryo development, and which are cleaned off during meiosis. Cloning retains these, and they can significantly affect anything from flower colour to whether a lamb's coat has straight or curly hair. Meristem - plants grow from the tip of a cylinder: the stem, root tips and so on. Just short of the tip is a stem cell which is a progenitor to all that follows on behind it: three layer-components, two kinds of vessel, woody and spongy filler cells and so on. This apparatus is called the meristem. It can be removed - usually from a root tip - and, in most flowering plants, induced to reproduce into an amorphous mass called a callus. Under further prodding with hormones, the callus will differentiate into meristems, that grow on to become fully adult, identical plants. (Subject to the caveats about epigenetics, given above.) ______________________________ Oliver Sparrow +44 (0)20 7736 9716 www.chforum.org _______________________________________________ the OrchidGuide Digest (OGD) orchids@orchidguide.com http://orchidguide.com/mailman/listinfo/orchids_orchidguide.com
