on 12/29/00 8:19 PM, [EMAIL PROTECTED] at [EMAIL PROTECTED] wrote:Xantusidae, Teidae, and I think a specie of Bascilus is known to do it.
This is known from geckoes,
At least 65 species are known to be parthenogenetic, at least in some populations (this does not include the snakes that switch to parthenogenesis late in life). One very interesting species that is entirely female is the blind snake Rhamphotyphlops braminus. This species is interesting because it can either be egg-laying, or live-bearing. Apparently most are egg-layers, but they can "opt" for live-bearing at times... always without a mate.
Another interesting thing about the species is that it is assigned to this genus. The genus Rhamphotyphlops is defined mostly on hemipenal characters... which females don't have. There are a few scale characters that define it too, but those are less rigorous.
Parthenogenesis is more complicated than an egg (the haploid gamete of the female) dividing on its own though. If that were the case, all offspring would have half the genetic material of the mother and we'd eventually have a cell with only 1 chromosome. Parthenogenesis can follow two main pathways. One is that Meiosis is incomplete, arrested at the end of Meiosis I, resulting in two diploid daughter cells that in some instances begin to divide (at least one strain of lab mouse does this, but not full term). The other is to have daughter-cell fusion at the end of Meiosis II which results in another diploid cell that can develop also. this is essentially auto-fertilization and is probably the more common of the two and could be potentially what facultative parthenogenetic snakes do (live-bearing snakes that are normally sexually reproducing CAN, late in life, switch to parthenogenesis and produce all male offspring). It is important to note that, statistically, neither of the examples of how to do parthenogenesis will result in offspring that are completely 100% genetically identical to each-other. There are many built-in mechanisms to prevent this from happening, even in sexually reproducing species (the likelihood of 2 identical sperm being produced by the same male is slime which is why even very large families with the same parents do not produce identical offspring, except for twins). Mechanisms include spontaneous mutation (rate of roughly 1/billion nucleotides in eukaryotic cells, so roughly 6 per cell division in humans!... mostly neutral and/or corrected automatically, except when making gametes), independent assortment of chromosomes in Meiosis I, crossing over in Prophase I, etc.
--
Gregory J. Watkins-Colwell
Dept. of Biology
Sacred Heart University
5151 Park Avenue
Fairfield, CT 06432
and
Yale Peabody Museum
Dept. of Vertebrate Zoology
170 Whitney Ave
PO Box 208118
New Haven, CT 06520-8118
