Let’s Do the Math Again
Earlier today I criticized Calvin College biologist Steve Matheson’s incorrect view of “junk” DNA. Matheson had argued in February that the human genome contains about 190,000 introns (stretches of non-protein-coding DNA that interrupt protein-coding genes), of which “only a handful” had important functional roles. “How many? Oh, probably a dozen,” he wrote, “but let’s be really generous. Let’s say that a hundred introns in the human genome are known to have ‘important functional roles.’ Oh fine, let’s make it a thousand.”
On the contrary, I pointed out that at least 90% of genes are alternatively spliced, meaning that 0.9 x 190,000 = 171,000 introns are involved in alternative splicing, an essential process that helps to ensure that the proper proteins are made at the correct developmental stage and in the appropriate cells and tissues.
Along comes University of Toronto biochemist Larry Moran, an outspoken Darwinist who hates the Center for Science and Culture so much he would probably heap abuse on us for saying that the Earth goes around the Sun. Sure enough, Moran wasted no time jumping on me for being an “Intelligent Design Creationist.” He posted the relevant portion of my critique and concluded: “It’s up to you, dear readers, to figure out all the things wrong with this explanation. You can start with the math. Arithmetic isn’t one of their strong points.”
So let’s do the math. Again. I will make the task easy for everyone–even Moran and Matheson:
Step 1. There are ~25,000 protein-coding genes in the human genome.
Step 2. There are 190,000 introns/25,000 protein-coding genes = 7.6 introns/gene on average.
Step 3. Ninety percent (possibly more) of gene transcripts undergo alternative splicing. Hence, 0.9 x 25,000 = 22,500 genes (actually, their RNAs) undergo alternative splicing.
Therefore, 22,500 genes x 7.6 introns/gene = 171,000 introns involved in alternative splicing.
This is just a rough estimate, of course. And as I wrote in my original critique of Matheson, even if I’m off by a factor of two we are still left with far more functional introns than Matheson acknowledges. This compels me to ask Steve Matheson: How exactly did you come up with your estimates? And what about you, Larry Moran? What sort of arithmetic are you using?