Thirty-one collections, representing perhaps ten species and seven unidentified collections, of Echeveria Series Racemosae from the Andes of Ecuador to Argentina are all polyploids, with gametic chromosome numbers from 44 to ~260. Their basic numbers are not apparent, but some probably have 16 or more alleles for each gene, and they can store a great deal of genetic heterozygosity. At metaphase I of meiosis nearly all cells of most collections have a few unpaired chromosomes and/or multivalents. One or a few chromosomes lag behind at anaphase I and are probably lost. Despite these irregularities, they are buffered by their many alleles for each gene; plants with one or a few extra chromosomes, or a few too few chromosomes, evidently survive and reproduce. Their populations must include plants that do not all have exactly the same chromosome numbers or the same dosages of every kind of gene. In cultivation they hybridize readily with each other and with Mexican Crassulaceae, and collectively they are part of a comparium of North and South American Crassulaceae that includes more than 200 species. At meiosis in their hybrids the corresponding chromosomes of the multiple sets from each polyploid parent form pairs preferentially with other chromosomes that came from the same parent. This shows that they are autopolyploids and, unlike allopolyploids, any different alleles of their multiple genes can be shuffled freely at meiosis and reapportioned in any combination. This allows them to undergo rapid rates of genetic recombination, thereby greatly increasing chances of adapting to rapid changes in geology and climate of the Andes during the Pliocene and Pleistocene. This should offer an evolutionary advantage to small plant populations.
You have requested a machine translation of selected content from our databases. This functionality is provided solely for your convenience and is in no way intended to replace human translation. Neither BioOne nor the owners and publishers of the content make, and they explicitly disclaim, any express or implied representations or warranties of any kind, including, without limitation, representations and warranties as to the functionality of the translation feature or the accuracy or completeness of the translations.
Translations are not retained in our system. Your use of this feature and the translations is subject to all use restrictions contained in the Terms and Conditions of Use of the BioOne website.
Vol. 2007 • No. 13