Question

$J.H$. Taylor's experiment which proved that $DNA$ replication is semi-conservative, was done on

• A. salivary gland cells of Drosophila melanogaster
• B. root tip cells of Vicia faba
• C. oocyte of Periplaneta americana
• D. cells of Neurospora crassa

Answer 1

Answer: (B)

root tip cells of Vicia faba

Answer 2

Taylor et al. $(1957)$ fed dividing cells of root tips of broad bean (Vicia faba) with radioactive $^3H$ containing thymine instead of normal thymine. Thymine is incorporated into $DNA$ which is the structural element of chromosomes. Taylor et al. found that all the chromosomes became radioactive. Labelled thymine was then replaced with normal one. Next generation was observed with radioactivity in one of the two chromatids of each chromosome while in subsequent generation radioactivity was present in $50\%$ of the chromosomes. This is possible only if out of the two strands of a chromosome, one is formed afresh while the other is conserved at each replication. Thus, the experiment proved semiconservative $DNA$ replication.