(1–2%), G. arboreum and G. herbaceum (together, ~1%). Many varieties of cotton have been developed by selective breeding and hybridization of these species. Experiments are ongoing to cross-breed various desirable traits of wild cotton species into the principal commercial species, such as resistance to insects and diseases, and drought tolerance. Cotton fibres occur naturally in colours of white, brown, green, and some mixing of these. Selected species Subgenus Gossypium Gossypium anomalum Wawra & Peyr. Gossypium arboreum L. – tree cotton (India and Pakistan) Gossypium herbaceum L. – Levant cotton (southern Africa and the Arabian Peninsula) Subgenus Houzingenia Gossypium raimondii Ulbr. – one of the putative progenitor species of tetraploid cotton, alongside G. arboreum Gossypium thurberi Tod. – Arizona wild cotton (Arizona and northern Mexico) Subgenus Karpas Gossypium barbadense L. – Creole cotton/Sea Island Cotton (tropical South America) Gossypium darwinii G.Watt – Darwin's cotton (Galápagos Islands) Gossypium hirsutum L. – upland cotton (Central America, Mexico, the Caribbean and southern Florida) Gossypium mustelinum Miers ex G.Watt Gossypium tomentosum Nutt. ex Seem – Maʻo or Hawaiian cotton (Hawaii) Subgenus Sturtia Gossypium australe F.Muell (northwestern Australia) Gossypium sturtianum J.H. Willis – Sturt's desert rose (Australia) Formerly placed in genus Gossypium Gossypioides brevilanatum (Hochr.) J.B.Hutch. (as G. brevilanatum Hochr.) Gossypioides kirkii (Mast.) J.B.Hutch. (as Gossypium kirkii Mast.) Kokia drynarioides (Seem.) Lewton (as G. drynarioides Seem.) Gossypium genome A public genome sequencing effort of cotton was initiated in 2007 by a consortium of public researchers. They agreed on a strategy to sequence the genome of cultivated, allotetraploid cotton. "Allotetraploid" means that the genomes of these cotton species comprise two distinct subgenomes, referred to as the At and Dt (the 't' for tetraploid, to distinguish them from the A and D genomes of the related diploid species). The strategy is to sequence first the D-genome relative of allotetraploid cottons, G. raimondii, a wild South American (Peru, Ecuador) cotton species, because of its smaller size due essentially to less repetitive DNA (retrotransposons mainly). It has nearly one-third the number of bases of tetraploid cotton (AD), and each chromosome is only present once. The A genome of G. arboreum, the 'Old-World' cotton species (grown in India in particular), would be sequenced next. Its genome is roughly twice the size of G. raimondii'''s. Once both A and D genome sequences are assembled, then research could begin to sequence the actual genomes of tetraploid cultivated cotton varieties. This strategy is out