The experimental control of chromosome pairing inFritillaria
The application of high temperatures or colchicine at early prophase reduces the metaphase chiasma frequency inFritillaria Meleagris. The reduction by heat is correlated with an increased proximal localization of such chiasmata as do form, whereas under colchicine, this localization is destroyed. It is inferred that heat acts by advancing the time limit to pairing, leaving the strongly procentric pairing type unchanged. Colchicine, on the other hand, by destroying the advantage that the centric regions have in pairing, leads to a slower, uncontrolled and highly variable pairing. Contact takes place at any point along the chromosome, sometimes at two or three independent points. This latter type of pairing leads to frequent interlocking. The action of colchicine is probably due to its specific inhibitory effect on the centromere.
The normal localization inFritillaria therefore seems to depend on two factors:
An early time limit to pairing.
A centromere control of the contact points of the pairing chromosomes.
Volume 100, 2021
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