"Cultivated species N. tabacum is an amphidiploid (2n=4x=48) evolved through the interspecific hybridization of the ancestors of N. sylvestris (2n=2x=24, maternal donor) and N. tomentosiformis (2n=2x=24, paternal donor) about 200,000 years ago."
The numbers below are haploid numbers, what you would see in an ovum or a pollen grain. The plants' diploid chromosome number, what you see in other plant tissues, is double that.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1086129/pdf/pnas01807-0011.pdf
Both N. rustica and N. tabacum appear to have arisen when the reproductive cells of both of the "parent" species (the male and the female) for each of them failed to segregate during meiosis, during which the diploid number is normally reduced to a haploid set of chromosomes, prior to the pollination event. The result was a double dose of chromosomes from both parents. The surprise is that the resulting offspring was more "fit" than either parent. This tetraploidy in the offspring produced the large-leaf plants of N. tabacum. I don't know much of the detail for N. rustica.
Bob
The numbers below are haploid numbers, what you would see in an ovum or a pollen grain. The plants' diploid chromosome number, what you see in other plant tissues, is double that.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1086129/pdf/pnas01807-0011.pdf
Both N. rustica and N. tabacum appear to have arisen when the reproductive cells of both of the "parent" species (the male and the female) for each of them failed to segregate during meiosis, during which the diploid number is normally reduced to a haploid set of chromosomes, prior to the pollination event. The result was a double dose of chromosomes from both parents. The surprise is that the resulting offspring was more "fit" than either parent. This tetraploidy in the offspring produced the large-leaf plants of N. tabacum. I don't know much of the detail for N. rustica.
Bob