Genetic systems in Allium

Summary

• 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.