6. Genes between related organism exhibits high variation. The variations would be maximally observed in
(1) Exons                                                      (2) Intron
(3) Promoters                                                (4) Polyadenylation site

Where Is Genetic Variation Highest in Genes? Introns Lead the Way

Genetic variation is the foundation of evolution and biodiversity. When comparing related organisms, scientists observe that some regions of genes exhibit more variation than others. Understanding where this variation is maximally observed not only informs evolutionary biology but also impacts genetics, medicine, and biotechnology. Among the gene regions—exons, introns, promoters, and polyadenylation sites—which one harbors the most variation between related organisms?

Gene Structure: Exons, Introns, Promoters, and Polyadenylation Sites

• Exons are the coding sequences of genes that are translated into proteins.

• Introns are non-coding sequences found between exons; they are removed during RNA processing.

• Promoters are regulatory DNA regions upstream of genes, controlling the initiation of transcription.

• Polyadenylation sites signal the addition of a poly(A) tail to mRNA, affecting stability and export.

Why Do Introns Show Maximum Variation?

Introns are the primary regions where genetic variation accumulates between related organisms. Here’s why:

• Lack of Selective Pressure:
  Introns do not code for proteins, so most mutations in these regions do not affect the organism’s fitness. This allows neutral mutations to accumulate freely over generations.

• Higher Mutation Tolerance:
  Mutations in exons can disrupt protein function and are often eliminated by natural selection. In contrast, intronic mutations are less likely to be harmful, so they persist and increase genetic diversity.

• Comparative Genomic Evidence:
  Studies consistently show that introns exhibit much higher sequence variability than exons or regulatory regions. This makes introns valuable markers for studying evolutionary relationships and population genetics.

How Do Other Regions Compare?

• Exons:
  These regions are under strong selective pressure to maintain protein function. Harmful mutations are quickly purged, resulting in lower variation.

• Promoters:
  While promoters can tolerate some variation, changes here often affect gene expression and are subject to selection.

• Polyadenylation Sites:
  These are short, functionally important sequences with little room for variation, as changes can impact mRNA stability and gene expression.

The Evolutionary Significance

Intronic variation provides a “neutral” record of evolutionary history, making introns ideal for studying genetic drift, population structure, and phylogenetic relationships. In contrast, exonic and regulatory regions are more conserved due to their functional constraints.

Conclusion: Introns Are the Hotspots of Genetic Variation

When comparing genes between related organisms, introns are the regions where maximum genetic variation is observed. This is due to their non-coding nature and tolerance for mutations, allowing them to serve as rich sources of evolutionary information.

Correct answer:
(2) Intron