What is the genomic constitution of old-world varieties of cotton (Gossypium arboreum, G. herbaceum) and new world varieties (G. hirsutum, G. barbedens) A. All diploids B. All triploids C. Old world 3n and new world 2n D. Old world 2n and new world 4n
Hint:Gossypium is a plant from which we get cultivated cotton. Most of these have diploid genetic constitution while five species have tetraploid constitution.
Complete answer:Gossypium is a genus belonging to the mallow family of Malvaceae. These are flowering plants from which cotton is harvested. In the tropical and subtropical regions of both old and new worlds, these species are found. Gossypium plants have about 50 species. Hence, it is the largest genus in the Gossypieae tribe. Still, more species are being discovered. The wild cotton species of this genus have a diploid constitution (2n). In the new world species, which are found in America and the Pacific islands (G. hirsutum, G. barbedens) are tetraploid (4n).
Additional information:Gossypium arboreum var. neglecta, locally known as "Phuti karpas", is the variety used to make Muslin in Bangladesh. The variation could only be grown in regions south of Dacca, along the banks of the Meghna River. It could be spun so that individual threads could maintain tensile strength at counts higher than any other variety of cotton G. herbaceum has high stems that grow 2 feet to 6 feet high with wide, hairy leaves. Their flowers are very small and yellow in color with a purple center. The plant exhibits extrafloral nectaries .
So, the correct option is D. Old world 2n and new world 4n.
Note: The difference in the genetic constitution is due to a single hybridization event nearly 1.5-2 million years ago. This genetic diversity can be exploited to broaden the genetic base of cotton.