Figure 1.

The evolutionary history of diploid and tetraploid Gossypium, as inferred by numerous chloroplast and nuclear data sets (Seelanan et al. 1997; Small et al. 1998; Cronn et al. 2002). Genome groups designate closely related species, as determined by interspecific meiotic pairing and chromosome size (Endrizzi et al. 1985). All diploid species have the same base chromosome number (n = 13); however, each genome group varies in genome size (1C content indicated in circles). Polyploid species are thought to have originated 1–2 Mya, following divergence of their diploid progenitors 5–10 Mya.