Abstract
By means of β-merkaptoethanol a distinct increase of endoreduplications in blood cultures of human origin can be produced. Such merkaptoethanol-induced endoreduplications were the object of morphological research and experiments concerning the pattern of DNA-synthesis.
Merkaptoethanol-induced endoreduplications are to a high degree similar to spontaneous endoreduplications both in morphology and function. In the chromosomes formed into pairs in endoreduplication (socalled diplochromosomes) morphologically distinguishing marks are always equally developed (e.g. secondary constrictions, division of the centromere). Even twists of the chromatids within a chromosome are to be found in a like manner in the other partner of the diplochromosome.
Endoreduplication consists of two successive DNA-replications without mitosis between.
If H3-thymidin is incorporated during the first DNA-replication the respective chromatids of the diplochromosome lying at the outside are labelled in metaphase whereas all the chromatids of the diplochromosomes are labelled, if H3-thymidin is incorporated during the second reduplication.
The “lying outside” of the labelled chromatids allows the conclusion that (1) there is a regular distribution of half-chromatids during the DNA-replication. In addition to that the must be (2) a difference concerning the affinity between certain chromatids, which causes the single chromosomes of diplochromosomes to lie in a certain order to each other during the preparation of the chromosomes.
A knowledge of these relations may be useful to set up a model of the chromosome.
Zusammenfassung
An durch β-Merkaptoäthanol induzierten Endoreduplikationen in Blutkulturen wurden morphologische und autoradiographische Untersuchungen angestellt. Merkaptoäthanolinduzierte Endoreduplikationen gleichen sowhl in morphologischer als auch funktioneller Hinsicht weitgehend spontan auftretenden Endoreduplikationen. Auf das identische Verhalten der Chromosomen des einzelnen Diplochromosoms in verschiedenen Eigenschaften (Zentromer, sekundäre Konstriktionen, Verdrehungen der Chromatiden) wird besonders hingewiesen. Die Endoreduplikation besteht aus zwei aufeinanderfolgenden DNS-Synthesen ohne Kernteilung dazwischen. Wird in der ersten Synthese H3-Thymidin eingebaut, so finden sich in der späteren Metaphase jeweils die “außen” gelegenen Chromatiden des Diplochromosoms matkiert. Dieses Verhalten und seine Bedeutung für das Verständnis der Chromosomenreplikation wird diskutiert.
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Schnedl, W. Geregelte Anordnung der Chromatiduntereinheiten in den Diplochromosomen bei der Endoreduplikation. Hum Genet 4, 140–152 (1967). https://doi.org/10.1007/BF00291259
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DOI: https://doi.org/10.1007/BF00291259