Further Data on Linkage inGammarus Chevreuxi; and its Relation to Cytology

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Abstract
1. In the Amphipod Gammarus chevreuxi, the cross-over value between the loci of two mutant genes (red and albino), for the 4528 offspring of 33 pair matings continued for 3 to 10 broods, was 44.69 per cent. 2. The haploid number of chromosomes is about 20; they are small, round, or ovoid. 3. In view of the small size of the chromosomes in G. chevreuxi, it is concluded that the cytological basis of crossing-over in this species is probably different in essential respects from that found in Drosophila, where it appears that a considerable actual length of chromosome must separate loci before they can show high cross-over values. Work is being continued on the subject. 4. In addition to the effect previously reported to be exerted by temperature on crossing-over in this species, it is found that age also modifies the process. The percentage of crossing-over is low in the first three broods, and rises later. This is the reverse of what is found in Drosophila.

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