What Are the Differences Between Neofuctionalization and Subfunctionalization?

Introduction

The generalization made by Theodosius has been validated by recent progress in the field of molecular biology and biochemistry. All modern organisms have been derived from common ancestor by a series of small changes, each change is attributed a selective advantage over the other, this is strongly supported by the similarity of their metabolic pathways and gene sequences across the phyla.

Occasional inheritable mutations yield organisms that are suited for better survival in ecological niche and progeny that are preferentially selected. This process of mutation and selection is the basis for the Darwinian evolution that led from the first cell to all modern organisms.

Neofunctionalization

After the event of gene duplication copy or paralog of the original gene is produced. While the original gene retains its ancestral function the paralog diverges to attain a whole new function different from the original one. This whole process of gene duplication is known as neofunctionalization.

It is a type of adaptive mutation wherein the duplicate gene acquires a whole new function which was not present in the original one. The new function acquired by the duplicate gene is due molecular changes that help this gene to take up new function. This change was proposed to be the root cause of divergence in organisms.

The Process

It all starts with the process of gene duplication, which is a result of defence mechanism against adverse environmental condition consequently leading to production of two genes, first is original one that retains the ancestral function and the second is the duplicate one which does not inherit the ancestral function instead gets a new function which protects the gene from adversity.

This new function adopted by the gene if proves to be useful will be selected by natural selection and will be inherited to next generation and remain fixed with the given population. The new function to the duplicate gene is attributed due to the redundancy of the ancestral gene.

One more reason for the new function is due to changes in the regulatory sequences or changes in coding region, but the formation of duplicate gene with new function does not affect the formation of the proteins or enzyme action.

Example of Neofunctionalization

One of the classic examples of neofunctionalization is the capability of Antarctic zoarcid fish to withstand freezing condition in Antarctic region. Antifreeze protein gene III was formed as a result of duplication of sialic acid gene. This new gene imparted a new property to withstand freezing depression and allowed them to survive in extremely cold condition of Antarctic.

Sub Functionalization- An Overview

During the process of gene duplication, original remains as it is with the ancestral function and a duplicate called paralog is produced which can have a different function from that of original one.

In case of sub functionalization, no new function is attributed and hence no new adaptations are formed. But the new gene which is formed help the ancestral gene to perform its function that is it sub functions with the original gene. In such types of gene duplication division of labour can be seen.

Differences appear when one of the gene is silenced segmentally leading to the deletion of one of the functions, so only duplicate gene is left with only one function out of the two. What should be noted is the fact that original gene had the ability to perform both the tasks but due to loss of original gene, the duplicate is left with only one function.

Examples of Sub Functionalization

One of the important examples of sub functionalization is formation of oxygen carrying pigment or haemoglobin cluster in human beings. During the evolution of vertebrates, the gene encoding this protein has been duplicated several times by various means. Initially, the ancestral gene and duplicate gene performed same function but during the course of changes both genes diverged which were required for normal function of the organism.

Difference Between Neofunctionalization and Sub Functionalization

Neofunctionalization	Sub Functionalization
Gene duplication takes place, and the duplicate gene acquires the new function and old one retains its ancestral function.	Gene duplication takes place followed by the segmentation of gene which results in the sharing of the functions.
No division of labour can be seen.	There is a division of labour.
These types of gene duplication result in adaptive evolution to survive under given environmental condition.	These types of gene duplication give rise to divergent evolution and formation of new species related to ancestral species.
Difference in the function can be observed immediately after duplication and in presence of ancestral gene.	Sub functioning of the gene can be seen once the ancestral gene is silenced.
Example of neofunctionalization is the development of antifreeze protein in Antarctic Zoarcid fish.	Example of sub functionalization is the formation of haemoglobin cluster in humans.

Conclusion

It has been proposed that both neofunctionalization as well as sub functionalization led to evolution. But after study of various models have proved that it is the sub functionalization that is the actual reason for the divergent evolution of various species. The evidence being the occurrence of related genes in similar species.

But it is also evident that neofunctionalization helped organisms to adapt well at a given environmental condition. Even though they both vary from one another, but both have led to evolution of modern organisms by changing the molecular make up.