What Does Functional Divergence Mean?

Introduction

Evolution is the basic key which can explain how human and other organisms appeared on Earth. Evolution can be defined as study of origin and development of various organisms on Earth. Organisms have evolved due to major morphological and functional changes. In the due course of evolution genes that are responsible for imparting various characters kept on adding by duplication of original gene. Some duplicate genes acquired new functions, whereas some just helped the ancestral gene to perform its function. These minor changes brought about major impact on development of organisms and new species evolved.

This development of new function due to duplication which is completely different from the ancestral function is known as functional divergence.

Gene Duplication a Major Contributor of Functional Divergence

Sometimes due to mutations duplication takes place which leads to introduction of second copy of whole gene into the chromosome due to defective replication. No deletions take place in the second copy, and it is superfluous which leads to evolution of new genes with new function while retaining the original gene and its function. This whole process of evolution is known as evolution by gene duplication.

Once a gene is duplicated one of the three things can happen to it −

• The duplicate gene produced does not have a new function, but it is preserved for evolution later, this process is known as sub functionalization.

• The duplicate gene acquires a new function whereas the original gene retains its old function, this process is known as neo functionalization.

• The duplication that is detrimental in nature is lost that causes neither the retention of old function nor the development of new function.

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.

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

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 hemoglobin 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.

Other Reason for Functional Divergence

• Functional divergence not only results from gene duplication but may also result due to chromosome or genome duplication.

• It may result from horizontal gene transfer that is commonly seen in bacteria and some other microorganisms.

Significance of Functional Divergence

• High degree of niche differentiation and low resource competition is caused as a result of high functional divergence.

• Some of the very important components of human body like hemoglobin, myoglobin, expanded form G-protein alpha subunit has resulted due to functional divergence.

• It provides new functions altogether to a gene which is formed by duplication, and the function which is entirely different function leading to divergent evolution.

• Some processes like Neofunctionalization helps the organisms to withstand harsh environmental condition.

• It also measures the distribution of a community towards the extremities of occupied functional trait space.

Conclusion

Different theories were proposed by many scientists to explain the theory of evolution. But evolution by gene duplication is one of the most widely accepted theory among all. Gene duplication causes the formation of a copy of the original gene.

Sometime this duplicate gene will have an entirely different function from that of ancestral gene or will subfunction with the original gene or sometimes may be totally deleted. In any of the cases there will be development of new function different from ancestral function, which is known as functional divergence and these differences in the function led to evolution of new species with different proteins adapted to perform under different condition.