A) DNA replication is continuous
B) DNA replicates in discontinuous manner
C) Chromosomes show semiconservative replication
D) DNA replicates in conservative manner
Correct Answer: C
Solution :
Taylor used root cells broad bean (Vicia faba). The root cells in cell cycle were kept in H-labelled thymidine medium and allowed to grow, so that it is incorporated into the S-phase DNA. Then the same cells in a cell cycle are kept on a medium with normal thymidine and allowed to grow again. The metaphase-chromosomes (maximum shortening and the known X-shaped) were then by autoradn graphy visualised and viewed under the microscope. The metaphase chromosomes after the first cell cycle in the medium with H-labelled thymidine was radioactively labelled in both chromatids. The two strands of parental double-standed DNA that is served as a template respectively, to a new strand (in this case with labelled thymidine was synthesised). After the second cell cycle on the medium with normal thymidine only one chromatid of metaphase chromosomes was usually radioactively labelled, the other not. This means, that each consists of a chromatid, and the DNA strand is replicated semi-conservative.
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