Ist der chromosomale Strukturpolymorphismus vonDrosophila Subobscura stabil oder flexibel?

Summary

• 1. Changes of the frequencies of different gene arrangements in populations ofDrosophila subobscura near Vienna in a periode of ten years could be observed.

• 2. The changes are restricted to the chromosomes J and U. The values of degree of heterozygousity, mean number of inversions and the index of free recombination, however, show no changes between the years.

• 3. Calculations were carried out in order to detect interchromosomal interactions between the various heterokaryotypic and homokaryotypic combinations. No significant differences between the calculated and the observed values could be found. The chromosomal polymorphism of different chromosomes is independent.

• 4. The speciesDrosophila subobscura represents the type of rigid polymorphism. The puffering ability of local populations could be due to the fact that all of the five long chromosomes are polymorphic. An unfavourable condition in one chromosome could be pretected by favourable conditions in the others.

• 5. The north-south cline in the frequencies of the standard gene orders of all chromosomes shows that extreme environmental changes, however, can not be puffered by the system.