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

Updated On: Jul 28, 2022

salivary gland cells of Drosophila melanogaster
root tip cells of Vicia faba
oocyte of Periplaneta americana
cells of Neurospora crassa

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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.

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Concepts Used:

The Molecular Basis of Inheritance

DNA Replication:

DNA synthesis is commenced at particular points within the DNA strand referred to as ‘origins’, which are certain coding regions. There are numerous origin sites, and when replication of DNA starts, these sites are mentioned as replication forks. Within the replication, the complex is the enzyme DNA Helicase, so that they can be utilized as a template for replication. DNA Primase is another enzyme that's essential in DNA replication.

RNA:

Ribonucleic acid (RNA) is an essential biological macromolecule that exists all together in biological cells. It is principally involved in the synthesis of proteins, that carry the messenger instructions from DNA, which itself contains the genetic instructions needed for the event and maintenance of life. In some viruses, RNA, in spite of DNA, carries genetic information.

Genetic Code:

Genetic code is the term we use in the manner that the four bases of DNA--the A, C, G, and Ts--are strung together in a way that the ribosome, the cellular machinery, can read them and switch them into a protein. In the ordering, every three nucleotides during a row count as a triplet and code for one amino alkanoic acid.

Read More: Molecular Basis of Inheritance

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	List-I		List-II
(a)	Gene ‘a’	(i)	β-galactosidase
(b)	Gene ‘y’	(ii)	Transacetylase
(c)	Gene ‘i’	(iii)	Permease
(d)	Gene ‘z’	(iv)	Repressor protein