An Outlook: The Importance of One-Tenth of One Percent

[Note: My daughter and son-in-law were in town this weekend and I had a presentation to do for the Door County Historical Society, all of which left my brain in a mush – though I did have a great time – so I am reprinting an old column this week. The following originally appeared in the Feb. 20, 2001, issue of the Door Reminder, and it seems appropriate given that one of my bosses, Madeline Harrison, is expecting her first child at any moment.]

Last week, two separate reports on the Human Genome Project were made public. During the course of reading about these reports and scanning through the limited amount I was able to grasp from the full reports (published in Nature 2/15/2001 and Science 2/16/2001) I have come away with one absolute reaction: humility.

The aspect of both reports that received the most attention in the media was the number of unique genes humans have within their genome. At the outset of the research it was widely anticipated that the number of genes would be around 100,000, and some estimates argued for more. The reality, however, is the relatively tiny number of 30,000. To put this into perspective, baker’s yeast has 6,000 genes and a fruit fly has 15,000.

As if the humbling of my species-oriented ego wasn’t enough, the report went on to deflate (pun very much intended) my male ego. Most of us remember at least something from our high school biology class (although my guess is that we probably remember the venereal disease films more than the frog dissections or the anatomy lessons) and one of the things we learned all those years ago is that women carry two X chromosomes while men carry an X and a Y chromosome. Human reproduction, in simplest terms, occurs when a male’s sperm fertilizes the female’s egg. The sperm can carry either an X or Y chromosome and when the X fertilizes the egg the result is a female baby, and when the Y fertilizes the egg, a boy is born. The odds of either result happening are always 50 percent.

To carry the reproductive refresher course a little further, all fetuses are female for the first seven weeks or so after fertilization occurs. At this point, if a sperm carrying the Y chromosome fertilized the fetus, a gene on the Y chromosome called SRY activates and starts the process of developing a male. The SRY gene also triggers another gene called MIS that dissolves the female portions of the fetus. In all, this SRY gene is only operative for a day or two and then, with its job done, it turns off and the fetus is on its way to becoming a male.

In comparison to the X chromosome, the Y chromosome is puny. Indeed, researchers have discovered that a significant portion of the Y chromosome is largely irrelevant, made up almost entirely of repetitive DNA sequences. The same researchers have stated that “males can do without” this portion of the Y chromosome. More than half the genes on the Y chromosome have counterparts on the X chromosome and one researcher referred to this portion of the chromosome as “living fossils.”

This all returns to the humility angle when we discover that the best scientific thought at the moment views the Y chromosome as a “decaying” X chromosome. That’s right, researchers now believe, based on their deciphering of the human genome to date, that at one time the Y chromosome very much resembled an X chromosome (if it wasn’t, in fact, identical). Indeed, the only thing that the Y chromosome really seems to excel at is sperm production. David Page, of the Massachusetts Institute of Technology, puts it this way: “Over eons, I think it [the Y chromosome] attracted genes that make sperm and offered them a haven…I think the male specificity of the Y has driven it toward functions that are good for men and not so good for women. Genes that make sperm fit that category. They’ve been tucked away on the Y chromosome.”

So, in essence, folks, males are largely sperm manufaturing plants. As far as I have been able to determine, in the limited time that I have had to reflect on this discovery, the knowledge that I am a manufacturing plant for sperm is only useful if I require a rejoinder to a woman who is complaining that she is simply a baby incubator. Other than this possibility, the knowledge that I am basically a sperm plant is rather distressing.

Equally distressing to learn from my readings is that males lead a highly precarious life largely because we have only one X chromosome. If there is a defect on one X chromosome in a woman, the healthy genes on the second X chromosome can often compensate for the defect. Men have no such luxury, thus we are susceptible to a variety of ailments passed directly to us through our mothers. Again, the only useful aspect to this knowledge is as a possible rejoinder to criticism from our mothers: “It’s not my fault, Mom. I must have been born that way [add calculated nod in mother’s direction here].”

Another thing I learned from my reading is that an average male makes enough sperm during his lifetime to repopulate the world several times over. Alternatively, an average woman creates only about 440 eggs during her lifetime. To put this another way, folks, there is an incredible amount of sperm going to waste in this world.

And finally, researchers on the human genome project have determined that the individual genomes of any two humans, anywhere on the earth, are 99.9 percent the same. In other words, on the genetic level, a Mongolian yak rancher and I are virtually the same. But that one-tenth of one percent can make a difference…a big difference.

Without that one-tenth of one percent I might actually be a regular attendee of monster truck rallies; I might actually care whether the Undertaker defeats the Rock at some World Wrestling match; or I might even own (and listen to!) Neil Sedaka albums.

And thus I close with heartfelt gratitude for that one-tenth of one percent.