Hey, there is one more clue we can add to the mix when considering introns. Let me quote from Puzzles of the Human Genome: Why Do We Need Our Introns? By L. Fedorova and A. Fedorov (Current Genomics, 2005, 6, 589-595):
One could argue that, in theory, removing “junk” DNA from the genome would have no negative effects on the organism. This has in fact happened in one vertebrate species, the puffer fish Takifugu rubripes, whose genome shrank several times millions of years ago . The general phenotype is essentially the same as that of closely related genera, even though it has lost vast sections of its genome.
Let’s now add this:
One advantage is that it is much faster to get from one end of a pufferfish gene to the other end and from one gene to the next when determining DNA sequence on continuous stretches of chromosomes. This is because the pufferfish genome is only about an eighth of the size of the human genome—400 million DNA bases. But the pufferfish is not deficient in its total number of genes. Rather, the pufferfish genome contains less of what seems to be irrelevant DNA, sometimes called “junk.” This junk DNA separates genes from one another like the space that separates words in a sentence. It also breaks genes into sections like syllables. The human genome is diluted with so much junk DNA that genes are contained in only three percent of it—compared to fifteen percent in the pufferfish.
So here are two vertebrates that have roughly the same number of genes, but while the human genome is filled with 3 billion nucleotides, the puffer fish genome is only 400 millions nucleotides long.
But here’s the catch.