Abstract
Polytene chromosomes of Chironomus thummi were stretched to their rupture in a pronase solution. A 176±26-fold elongation was achieved. The DNA compaction ratio, defined as the ratio of DNA length in a haploid set (85±5 mm) to the length of a polytene chromosome set (520±40 μm), was 164±22. Closeness of these two values demonstrates the uninemy of the chromatids of Chironomus chromosomes. The effect of ethidium bromide on the elastic properties of chromosomes prestretched in a pronase solution and the lengthening of these chromosomes after ethidium staining suggest that DNA molecules are double-stranded and supercoiled to the moment of the chromosome rupture. It is concluded that a Chironomus chromatid consists of a single DNA molecule (or of a single chain of linked DNA molecules) both ends of which are located in the telomeres.
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To the memory of Prof. Vera V. Khvostova
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Gruzdev, A.D., Reznik, N.A. Evidence for the uninemy of eukaryotic chromatids. Chromosoma 82, 1–8 (1981). https://doi.org/10.1007/BF00285745
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DOI: https://doi.org/10.1007/BF00285745