Page "Intron" Paragraph 48

Early studies of genomic DNA sequences from a wide range of organisms show that the intron-exon structure of homologous genes in different organisms can vary widely.

More recent studies of entire eukaryotic genomes have now shown that the lengths and density ( introns / gene ) of introns varies considerably between related species.

For example, while the human genome contains an average of 8. 4 introns / gene ( 139, 418 in the genome ), the unicellular fungus Encephalitozoon cuniculi contains only 0. 0075 introns / gene ( 15 introns in the genome ).

Since eukaryotes arose from a common ancestor ( Common descent ), there must have been extensive gain and / or loss of introns during evolutionary time.

This process is thought to be subject to selection, with a tendency towards intron gain in larger species due to their smaller population sizes, and the converse in smaller ( particularly unicellular ) species.

Biological factors also influence which genes in a genome lose or accumulate introns.