Genome Duplication
Natural And Artificial Polyploidy (2n, 3n, 4n, 5n, 8n, 12n)
The Xenopus genus includes various tetra-, octo- and dodecaploid species (Table 4) that were generated times over a period ranging from 80 to 10 millions years ago by interspecies hybridization through allopolyploidization (Evans et al., 2004) [11, 12]. These species offer a unique model to study the consequences of whole genome duplication (i.e., study the fate of duplicated genes). In addition, polyploidy animals can be generated easily in laboratory providing an ideal genetic marker. X. laevis tetraploid are produced artificially by subjecting diploid egg from isogenetic clones to hydrostatic pressure during the last meiotic division (Kobel, al., 1970; Chrétien al., 1996). Tetraploid cells can be distinguished from diploid cells by differences in their DNA content as well as by the number of nucleolar organizers. After surface staining with various mAbs and an APC-conjugated secondary reagent, cells are fixed and stained with propidium iodide to detect by flow cytometry differences in DNA amounts (Chrétien al., 1996; Turpen 2004). By using isogenetic clones rather than inbred strains to generate tetraploids, the progeny can be directly maintained by gynogenesis.
Existing Xenopus Species
| 2N (20) | 4N (36) | 8N (72) | 12N (108) |
|---|---|---|---|
| Xenopus (Silurana) tropicalis |
X. laevis X. mulleri X. borealis X. clivii X. fraseri X. gilli1 | X. vestitus X. amieti X. andrei2 X. vitei2 | X. ruwenzoriensis X. Longpipes2 |
1 Species almost extinct, a few individuals protected in South Africa (Capetown)
2 Species rare, a few live specimens are in Geneva, Switzerland