Gene

• It is the small segment of DNA located in a fixed place on the chromosome capable of inheritance of characters from one generation to another.
• The fine structure of a gene is given by different scientist.

• Among them, two main theories were proposed and are:

1. Old Theory
2. Modern theory

A. Old Theory of gene

• This theory explains the fact that the genes in a chromosome are arranged in a linear array stung like beads on an unfastened necklace.
• This theory is also called bead theory.
• It explains the fact that
• Gene is not sub divisible.
• Crossing over doesn’t take place within a gene but it occurs between two genes.

B. Modern theory of gene

• This theory was proposed by Benzor in 1950.
• He told that the Bead theory was not correct and proposed that the gene can be further divided.
• The gene has many nucleotide pairs where the mutation and recombination can occur.
• Such nucleotide base pair of a gene can act as muton and recon.
• He demonstrated his theory by his experiment on E. coli phase T­₄ .
• This phase T₄ is an obligate parasite which grow rapidly under the optimal condition provided to it and cause the lysis of the bacterial cell wall thus releasing more than 3000 progenes in 20-25 minutes.