Final answer:
Farmers have bred polyploid varieties to create new species with desirable traits such as higher yield and disease resistance, using this genetic mechanism as an adaptation tool to improve crops.
Step-by-step explanation:
Farmers have bred plants into polyploid varieties primarily because polyploidy can lead to new species with desirable attributes, acting more as an adaptation mechanism rather than an error. In particular, the production of allopolyploids has allowed for the creation of agricultural staples such as wheat, cotton, and tobacco plants by hybridizing two different species and then doubling the chromosome number. This process not only bypasses the sterility issue that often accompanies hybridization, due to the lack of homologous chromosome pairing during meiosis but also can combine and amplify the benefits from both parent species.
Crop improvement relies heavily on this genetic diversity and the introduction of new gene variants, which can lead to crops with increased yields, better taste, easier harvest, and importantly, resistance to diseases and pests. The Irish potato famine is a historical example demonstrating the dangers of low crop diversity and the necessity for maintaining crop biodiversity, underlining the importance of polyploidy in creating diverse, resilient crop varieties.