Taylor experiment (genetics)

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In genetics, the Taylor experiment is an experiment by the US molecular biologist James Herbert Taylor . In 1956 he investigated the replication mechanism of DNA with radioactively labeled nucleotides (building blocks of DNA ) . At the same time, Meselson and Stahl were also working on an experiment on the mechanism of DNA replication .

The attempt

For the experiment, Taylor used broad bean ( Vicia faba ) root cells . He let these cells grow for one cell cycle in a medium with 3 H -labeled thymidine so that it is incorporated into the DNA in the S phase. Then he let them grow again for one cell cycle on a medium with normal thymidine so that this was used for replication in the S phase.

The metaphase - chromosomes (maximum shortened and in the familiar X shape) were then by autoradiography visualized and viewed under a microscope.

Results

The metaphase chromosomes after the first cell cycle on the medium with 3 H -labeled thymidine were radioactively labeled in both chromatids. The two strands of the parental double-stranded DNA thus each served as a template strand on which a new strand (here with labeled thymidine ) was synthesized. After the second cell cycle on the medium with normal thymidine , mostly only one chromatid of the metaphase chromosomes was radioactively labeled, the other not. This means that each chromatid consists of a double strand of DNA and that this is replicated semi-conservatively.

After the second cell cycle, Taylor also observed chromosomes that were not "half-marked" or completely unmarked, but also those that were only marked in parts, so-called harlequin chromosomes . From this Taylor concluded that there are exchanges between chromatids in mitosis .

The Meselson-Stahl experiment only allows the statements that a) in DNA replication the molecules consist of 50% old and 50% newly synthesized DNA and that b) DNA replication proceeds according to the semiconservative mechanism, d. This means that each of the two parent strands is supplemented by a new daughter strand. Taylor was also able to demonstrate the semiconservative replication, but also derived a connection to the distribution of the mother / daughter strands in the chromatids.

Individual evidence

  1. ^ PC Hanawalt: Classic Perspective: Density matters: The semiconservative replication of DNA. In: Proceedings of the National Academy of Sciences . 101, 2004, pp. 17889-17894, doi : 10.1073 / pnas.0407539101 . Here the full text visible. Accessed September 15, 2013
  2. ↑ JH Taylor, PS Woods, WL Hughes: THE ORGANIZATION AND DUPLICATION OF CHROMOSOMES AS REVEALED BY AUTORADIOGRAPHIC STUDIES USING TRITIUM-LABELED THYMIDINEE. . In: Proc Natl Acad Sci USA . 43, No. 1, 1957, pp. 122-138. PMID 16589984 . PMC PMC528395 (free full text).
  3. ^ JH Taylor: Sister Chromatid Exchanges in Tritium-Labeled Chromosomes. . In: Genetics . 43, No. 3, 1958, pp. 515-529. PMID 17247775 . PMC PMC1209899 (free full text).