Taylor, Woods, and Hughes did an experiment in Vicia faba. They used radioactive

Question

Taylor, Woods, and Hughes did an experiment in Vicia faba. They used radioactive 3H-thymidine to label newly synthesized DNA in order to monitor the mechanism of replication. Their data, seen in the figure above, provided evidence for semi-conservative replication. Now predict what their results would have been if replication had been conservative or dispersive.

   a.  
In each sister chromatid, one DNA strand would be labeled, and the other would be unlabeled.

   b.  
In one sister chromatid, both DNA strands would be labeled. In the other sister chromatid, both DNA strands would be unlabeled.

   c.  
In each sister chromatid, parts of both strands would be labeled, other parts unlabeled.

   d.  
All of the above answers are possible.

Replication I Both sister H-thymidine chromatids labeled Unlabeled chromosome Metaphase Anaphase Chromatids migrate into separate cells Replication II Sister chromatid No sister chromatid exchange Unlabeled thymidine exchange (b) (c) Unlabeled chromatid Reciprocal regions of both Only one chromatids chromatid labeled labeled Metaphase II Metaphase

Explanation / Answer

b). In one sister chromatid, both DNA strands would be labelled. In the other sister chromatid, both DNA strands would be unlabelled. ---> Conservative replication

c). In each sister chromatid, parts of both strands would be labelled, other parts unlabelled. -----> Dispersive replication

In conservative replication, the original strands of DNA are not forwarded to the next generation, but it act as a temple for the synthesis of new DNA. So, both strands in the other sister chromatid would be unlabelled. In dispersive replication, the strands of DNA are intermittently labelled.

on, but it act as a temple for the synthesis of new DNA. So, both strands in the other sister chromatid would be unlabelled. In dispersive replication, the strands of DNA are inteemittently labelled.

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