Taylor conducted the experiments to prove semiconservative mode of chromosome replication on Vicia faba


In 1953, James Watson and Francis Crick proposed the double-helix structure of DNA. One of the key aspects of this structure was the complementary base pairing between the two strands. This led to the hypothesis that DNA replication occurs in a semiconservative manner, where each new DNA molecule consists of one original (parental) strand and one newly synthesized (daughter) strand.


Taylor conducted experiments to provide evidence for the semiconservative mode of chromosome replication. He chose Vicia faba (broad bean) as his experimental organism for these studies.


Taylor labeled the DNA of Vicia faba plants with two different isotopes of nitrogen: heavy nitrogen (15N) and light nitrogen (14N). The heavy nitrogen (15N) isotope is slightly heavier than the light nitrogen (14N) isotope. By using these isotopes, Taylor could distinguish between the parental and newly synthesized DNA strands.


1. Taylor allowed the Vicia faba plants to grow in a medium containing heavy nitrogen (15N) for several generations. This ensured that all the DNA in the plants incorporated the heavy nitrogen isotope.
2. Taylor then transferred the plants to a medium containing only light nitrogen (14N). This allowed the newly synthesized DNA to incorporate the light nitrogen isotope.
3. At regular intervals, Taylor extracted DNA from the plants and performed density gradient centrifugation to separate the DNA molecules based on their density.
4. The DNA molecules containing heavy nitrogen (15N) settled at a higher position on the density gradient, while the DNA molecules containing light nitrogen (14N) settled at a lower position.
5. Taylor observed the distribution of DNA in each generation to determine the mode of replication.


Taylor's experiments provided evidence for the semiconservative mode of chromosome replication. He observed that in the first generation after shifting to the light nitrogen (14N) medium, the DNA molecules showed a single band at an intermediate position on the density gradient. This indicated that each DNA molecule consisted of one heavy (parental) strand and one light (newly synthesized) strand.
With subsequent generations, Taylor observed two bands on the density gradient: one corresponding to the position of heavy nitrogen (15N) DNA and the other corresponding to the position of light nitrogen (14N) DNA. This confirmed the semiconservative replication of DNA.

Therefore, Taylor's experiments on Vicia faba provided strong evidence for the semiconservative mode of chromosome replication.