ISSN:
1432-0886
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Summary 1. The coiling of chromosome arms in Tradescantia shows L and R directions to be equally frequent (Table 6). 2. This is true of one chromosome arm (e.g. a unique telocentric) — and presumably of any one — in different cells. Coiling must therefore begin afresh in every cell division. 3. The direction of coiling in opposite arms of the same chromosome (across the centromere) is biassed: it is almost 3.5 times as frequent in the opposite as in the same direction. The combinations LL∶LR∶m RR are as 1∶7∶1 (Table 7). 4. The bias is perhaps greater in diploid than in tetraploid Tradescantia. 5. The directions of coiling in partner arms (across a terminal chiasma) where the chromosomes are similar are at random and without bias. The combinations LL∶LR∶ RR are as 1∶2∶ 1. This is true of the diploid and tetraploid in Tradescantia, of bivalents and multivalents, and probably of unpaired as well as paired, homologous arms. 6. Contrariwise, however, where the partner arms belong to unequal chromosomes (one-armed and two-armed) coiling across a chiasma is biassed. The bias is small but again it is in favour of unlike directions. The bias seems to be reduced when a third chromosome is added (Table 8). 7. A small test of the effects of varying external conditions gave negative results. 8. We conclude that: a) The equality of L and R frequencies may be universal. b) Bias of coiling relations across the centromere may be equally so. c) But in degree it is likely to vary under genotypic control. d) Bias across a chiasma perhaps arises only with structural hybridity.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00325981
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