Abstract
1) Origin of extra chromosomes in 8- and 9-chromosome rye plants, Secale cereale L., was karyomorphologically studied in this paper.
2) Eight chromosome plants (2n=16) were sometimes found in a variety “Korean” No. 1, which is normally 2n=14 of a2d1 type. Comparison of the karyotype of such plants with that of the normal suggested that the two extra chromosomes were derived from the fragments of a certain chromosomes, because the long arm of the extra chromosomes is quite the same in length as the short arm of the “b” chromosome. The karyotype of this form was designated as a2d1x, as that of the normal one being a2d1.
3) All of the plants of “Korean” No. 2 examined have eighteen or 2n=18 chromosomes in somatic cells, and in this material two “a2” and two fragments were observed besides the normal fourteen chromosomes. The “a2” chromosome is apparently duplicated, and the fragment shows the same figure as mentioned above. The extra chromosomes of these eighteen chromosome rye plants, therefore, may be arised by two types of chromosomal aberrations, namely, duplication and fragmentation. The karyotype of this form was shown as a2a2d1x.
4) It is convincing to the author that a pending problem concerning the origin of extra chromosomes in rye whether the extra chromosomes are originated from duplication or fragmentation of some chromosomes, has attained to a conclusion that the both cases are probable.
5) As two different karyotypes, a2d1x, and a2a2d1x, were here added to the previously found five types, that is, a1d1, a1d2, a2d1, a2d2 and a3d2, number of different karyotypes in rye amounted to seven.
