Funny you should ask that Christian.
The M gene also gives you the ability to know that a 1/2" wrench will fit a 12mm bolt in a pinch, or a 3/4" wrench is an exact match to a 19mm bolt (head size).
A 3/8" will fit a 10mm if you beat it really hard. The XYM gene is also the one that makes you want to spit, fart, laugh at the Three Stooges, pee outside, and blow things up. It also has a built in map and tracking device, so you never have to ask directions no matter how lost your wife thinks you are.
If an appliance or vehicle breaks down at your house, and you reach for a tool box instead of the telephone or checkbook, you most likely have the gene. What ever you do, don't get it confused with the XYD (dumb jock) gene. That one makes you memorize sports stats from a hundred years ago, and worry about the latest teams that have no affect on your life what so ever. It also makes you want to spit, fart, laugh at the Three Stooges, pee outside, and blow things up. The only thing is, they can't figure out how to actually make things blow up. That's how you tell the difference between the XYM and XYD genes. Both are similar to the XYN (Nascar) gene, but that's a whole new thread.
10,000 years ago we would have eaten you. Today, we drag you along and allow you to pollute the gene pool.