Molecular Basis of Inheritance
Nucleic acids are long polymers of nucleotides. While DNA stores genetic information, RNA mostly helps in transfer and expression of information. DNA, being chemically and structurally more stable, is a better genetic material. However, RNA is thought to have evolved first. DNA replicates semiconservatively. During transcription, one strand of DNA acts as template to direct the synthesis of complementary RNA. The genetic code is read again on the principle of complementarity by tRNA, which acts as an adapter molecule. Protein synthesis is done by ribosomes. Both transcription and translation are energetically very expensive processes. Regulation of gene expression refers to a very broad term that may occur at various levels. The genes in a cell are expressed to perform a particular function or a set of functions. Human Genome Project was a mega project that aimed to sequence every base in human genome. Many new areas and avenues have opened up as a consequence of the project.
The semiconservative nature of DNA replication in plants was proved by -
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Taylor and Colleagues
In semiconservative replication, each new DNA molecule keeps one old strand and gets one new strand. It was first proved in bacteria and then in the chromosomes of plants.
(1) Watson and Crick — Incorrect. They proposed the double helix structure of DNA. They did not prove the mode of replication.
(2) Matthew Meselson and Franklin Stahl — Incorrect. They proved it in 1958 in the bacterium E. coli, using heavy nitrogen, not in a plant.
(3) Taylor and Colleagues — Correct. In 1958 they used radioactive thymidine in Vicia faba (faba beans). This showed that the DNA of the chromosomes in plants also replicates semiconservatively.
(4) Hershey and Chase — Incorrect. They showed that DNA is the genetic material, using bacteriophages.
Note: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
NCERT Extract:
The Experimental Proof – …
