Chromosomes showing neocentric activity were identified with the aid of the C-banding technique in an inbred line of rye, 1940-129 of cv. 'Stålråg'. The frequency of cells with neocentrics varied from 34 to 35.7% at first anaphase, and from 32 to 68% at second metaphase. In most cells only one chromosome showed the activity. It always belonged to the group 4-5-6R, and in cells where individual identification of chromosomes was possible the activity was invariably located at the telomere of the arm 4RS. When in rare cases two or three chromosomes were active, one chromosome again belonged to the group 4-5-6R, the other was identified in four cells as a member of the group 2-3-7R, but it is possible that all the telomeres with a prominent C-band can occasionally show the activity. It is assumed that certain telomeric regions remain in the active state at both meiotic divisions and offer secondary accumulation sites for kinetochoric proteins.

SUMMARY -The karyotype and meiosis of wild and cultivated ulluco were analysed. All wild ulluco clones studied were triploids, 2n = 36, and all cultivated ones diploids, 2n = 24. A tetraploid cell line, 2n = 48 was found in a cultivated clone. Cultivated and wild ulluco have a similar set of chromosomes, with two pair of long, two pair of short and eight pair of intermediate chromosomes, and with two pair of satellite chromosomes. This indicates that the basic chromosome number of ulluco may be x = 6. Male and probably also female meiosis of diploid cultivated ulluco is regular and pollen stainability high. Reasons for the poor seed set of cultivated ulluco are to be looked for in other processes than meiosis. Meiosis of triploid wild ulluco is irregular, leading predominantly to aneuploid gametes. pollen stainability was low, and there was more variation in pollen size than in cultivated ulluco, most probably because of aneuploidy.

With the aid of C‐banding technique the sequence of the first meiotic prophase stages in the anthers of rye has been determined as follows: synizesis, pachytene, early diplotene, diffuse stage, second contraction, late diplotene, and diakinesis. The heterochromatic regions fuse together twice, during the formation of the synizetic knot and in the second contraction stage. After the second fusion, in diplotene and diakinesis prominent interchromosomal connections were always visible mainly between the heterochromatic regions of the bivalents. Similar fibers were also observed in diplotene‐diakinesis stages in Feulgen‐Giemsa stained preparations. Most of the interchromosomal connections seem to disappear before the first metaphase stage. The main function of the interconnections is suggested to keep the bivalents in contact to each other before the spindle fibers are formed.

VIINIKKA, Y. 1975. Allocyclic regions and banding patterns in the chromosomes of Najas marina. -Hereditas 81: 47-54. Lund, Sweden. ISSN 0018-0661. Received June 17, 1975 Seven spontaneous allocyclic regions have been observed in the prophase and prometaphase chromosomes of the first pollen mitosis in race B of Najas marina. Morphologically the allocyclicregions were similar to the cold-induced H-segments observed in some organisms. C-bands were shown to correspond to the allocyclic regions. In addition, after use of the C-banding method there were paired dots in the centromeric regions of all the six chromosomes. With quinacrine mustard staining the allocyclic regions were not differentiated in any way. However, with phase contrast microscope these regions were sometimes visible as unstained gaps when acetic acid treated chromosomes were stained with Feulgen. There were no allocyclic regions in B chromosomes. After C-banding two dark dots were also visible in the centromeric region of the B chromosome. The rest of this chromosome was stained as pale as the interband regions in A chromosomes. In this respect, the B chromosomes behave like facultative heterochromatin. It was proposed that both the formation of allolyclic regions and C-bands depend on the presence of a special protein component in these chromosome regions.

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