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60
nils nybom
lead to an over-representation of the extreme chromosome numbers
similar to what is observed in Datum, and it is possible that a
mecha-nism of the kind described here may be responsible even for this case
of non-random distribution of the extra chromosomes at tlie triploid
meiosis.
Acknowledge m e 11 t s. — 1 wish to thank Dr. A. Levan and
Dr. G. Östergren for valuable suggestions and for discussing this
problem.
Summary.
On the basis of a table published by Levan (1935) il is shown that the
distribution of a cerlain chromosome, the Si chromosome, is non-random at meiosis in
autotriploid Allium Schoertoprasum. In pollen grains with few chromosomes there
is a deficit of Si chromosomes, while there is an excess in pollen grains with many
chromosomes.
The cause of this non-random distribution is discussed and it is considered
that through a certain mechanism, the asymmelrieal spindle, the univalents at the
first division are preferably inclosed in the largest anaphase group.
Literature cited.
1. Beadle, G. \V. 1935. Crossing over near the spindle attachement of the X-chro-
mosomes in attached X-triploids of Drosophila melanogaster. — Genetics
20: 179—191.
2. Darlington, C. i). 1929. Chromosome Behaviour and Structural Hybridity in
the Tradescantiae. — J. Genet. 21: 207—28(5.
3. — 1937. Recent Advances in Cytology. 2nd ed. London 1937.
4. Darlington, C. D. and Mather, K. 1914. Chromosome Balance and Interaction
in Hyacinthus. — J. Genet. 46: 52—61.
5. Levan, A. 1935. Zytologische Studien an Allium Schoenoprasum. — Hereditas
22: 1—128.
6. Myers, W. M. 1944. The randomness of chromosome distribution at anaphase I
in autotriploid Lolium pcrenne L. — Bull. Torrey Bot. Club. 71:144—151.
7. Satina, S. and Blakesi.ee, A. F. 1937. Chromosome behaviour in triploids of
natura stramoniuin. I. The male gametophyte. —- Am. J. Botany 24: 518
527.
8. — 1937. II. The female gametophyte. Am. J. Botany 24:621—627.
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