Genetic systems in Allium

Abstract

1. Allium species show very little variation in the symmetry of their chromosomes within as well as between their complements. 2. In tetraploid A. macranthum and A. bidwelleae, the complement shows a distinct size differentiation of chromosomes into three groups (Fig. 1). 3. There are mainly six types of nucleolar chromosomes in the genus (Fig. 6). In some species they also carry heterozygosity (Figs. 7–9). 4. In A. stipitatum the heterozygous nucleolar chromosomes also show allocycly which is revealed at the room temperature. 5. Species with supernumerary B-chromosomes are all diploids except A. porrum. 6. There are three basic numbers, i.e. 7, 8 and 9, in the genus. North American species have seven as the basic chromosome number. Most of the Eurasian species have x=8 and a few x=7 and 9. 7. In the section Molium, a group of Mediterranean species, the basic numbers 8 and 9 have arisen from seven in the form of an ascending series, i.e. 7-----8-----9. In the section Codonoprasum which includes European and West Asiatic species, the basic number eight has given rise to both seven and nine.