By Dr Ananya Mandal, MD
The underlying concept of Genes has undergone rapid changes over the last few decades. It was originally thought as the unit of inheritance and simply a DNA based unit that converts to RNA and forms proteins that are essential for life. Genes were thought to form the blue print of an organism.
“One gene hypothesis”
Earlier it was believed that one gene makes one protein; the “one gene hypothesis”. This concept has undergone a sea change. This happened after it was found that genes were not single units but a long continuum and there was the concept of alternative splicing and trans-splicing. This meant that genes could split into fragments each coding for different proteins.
Locations of control regions of genes
In addition, as it was previously believed, control regions of a gene need not remain close to the coding region or exons and introns or somewhere upstream over the DNA or even on the same chromosome.
The discovery of these switches and coding regions that initiate and regulate the protein formation was the single largest discovery that helped in genetic research especially in its concept of disease causation and inheritance.
Spilianakis and colleagues found that promoter region of the interferon-gamma gene on chromosome 10 and the regulatory regions of the T(H)2 cytokine locus on chromosome 11 come nearer to each other because they may be jointly regulated.
There is evidence that shows that fused proteins may be coming from codes on two separate genes coding for separate genetic protein products. This is a more frequent phenomenon than previously believed and the exact role of these functional proteins is unknown. Some of the proteins or parts of the protein may be composed far away from the exons or even located on different chromosomes.
Refuting the “one gene hypothesis”
This has refuted the one gene hypothesis and has given rise to the definition of a gene as “a union of genomic sequences encoding a coherent set of potentially overlapping functional products.” This means genetic products, whether they be proteins or RNA, may have more than one specific or non-specific loci or locations and the regulatory DNA or promoter regions that regulate the RNA and protein coding are classified within the “gene associated regions”. These may be located within, near or further upstream from the coding regions or may be located on different chromosomes altogether.
Reviewed by April Cashin-Garbutt, BA Hons (Cantab)