What is Gene?
The word gene largely remained a puzzle for the earlier scientist. The term ‘Gene’ got its identity in different prospects at different points in time. In the Mendelian era, gene definition was limited to the substance carrying hereditary information. Later the definition was looking for the physical nature of the gene and the conclusion came in the form of the structure of nucleotide and models of DNA molecule. Still, the story was not complete as we needed to understand the correlation between the number of nucleotides in DNA and gene. The discussion eventually ended with the term Cistron proposed by Benzer.
Our earlier attempt to identify the gene or genetic material can be visualized from the work of Mendel. In the eyes of Mendel, a pair of Gene or Factor was responsible for a given character. ‘Factor’ is a carrier of hereditary information has been hypothesized way back in 1856. Unfortunately, Mendel’s work remained unnoticed till it was rediscovered in the year 1900 by Hugo de Vries, Carl Correns, and Erich von Tschermak. Later Morgan extended the work through his experiment on Drosophila and eventually established the Mendelian model of inheritance. However, still, its physical nature was yet to be deciphered.
With the basic patterns of genetic inheritance established, many biologists turned to investigations of the physical nature of the gene. The very first attempt to identify the nucleic acid was done by the young Swiss physician Friedrich Miescher who isolated and purified the nucleic acid from the nucleus of the cell and termed it as “Nuclein”.
However, the first noticeable attempt towards the search of the genetic material was Griffith’s Experiment. He worked with two strains of Diplococcus pneuminae and came with his transformation experiment. This experiment was performed in the year 1928 and it is often considered as the milestone for the commencement of molecular biology.
In 1941, George Wells Beadle and Edward Lawrie Tatum showed that mutations in genes caused errors in specific steps of metabolic pathways. This showed that specific genes code for specific proteins, leading to the “one gene, one enzyme” hypothesis
Though Griffith failed to explain the reason for the transformation, his experiment led to another milestone in 1944 when Avery, MacLeod, and McCarty provided concrete evidence for DNA being the genetic material. And finally, the Blender experiment of Hershey and Chase provided conclusive evidence in vivo condition that DNA is the genetic material.
Meanwhile, the structure of DNA was established by Watson and Crick double helix model in 1953, still, the question that what is the length of DNA that will constitute a gene remained unanswered. The answer to the question came from the term “Cistron” proposed by Benzer in 1957. One cistron is equivalent to the minimum number of nucleotides that code for a functional polypeptide or protein.
Reference:
https://www.amazon.in/BIOLOGY-MINDMAPS-CLASS-Exclusively-NEET-ebook/dp/B0865HQ986
