Mitochondria, Missing Links and the Real Feminine Mystique: Part I

It is common knowledge that we inherit half our genetic code from our one parent and half from the other.  Very democratic.  Both parents get an equal bite at the genetic apple. 

            Unfortunately, like much of what we take as common knowledge, there is wiggle room.  Among other things, you must remember that the “Y” chromosome that creates all males is just a truncated “X” chromosome.  That is what gives it the “y” shape it is named for.  A “y” is the feminine “x” without one of the branches.  That branch carries genetic code that is missing from the “y” gene.  The fact that the “x” carries more code is one of the reasons that some characteristics (baldness, color blindness, hemophilia…) tend to be passed on by our mothers, not our fathers. 

            And then there is mitochondrial DNA (mtDNA), which is only passed down by our mother’s.  In pop-science, this is called the “Eve” gene.  Science articles written for the mass market love terms like “Eve” gene and “God” particle.  They offer an emotional hook for readers who would otherwise tune out heavier words like “mitochondrial” and “Higgs boson.”  [There is nothing like sexing up the science to get a wider audience.]

            Mitochondrial DNA probably started out as a parasite.  It is a circular strand encapsulated in tubular packets within our cells.  It may have originally started as a living entity with its own DNA.  It had the ability to enter other nucleated cells—like ours.  There it traded its one outstanding characteristic—the ability to create energy disproportionate to the energy it took from the environment—for a snug, homey environment.  Slowly (which is about the only speed evolution takes) this foreign DNA became our own.  But it also has another super power, it transfers itself only through the female line.  My mitochondrial DNA came only from my mother, her mother and her mother before her.  It is transferred only to my daughters, and they have passed it to their girls.  We are an unbroken line of female-only, mother-to-daughter lineage going back for the approximately 300,000 years since homo-sapiens appeared on this earth.  I may have gotten these baby blue eyes from Dad, but my hidden mitochondria is only from Mom.

            Men do have mitochondrial DNA.  They got it from their mothers, just like I did.  But they can not pass it on to their sons or their daughters.  Why?  Because the sperm that carry the male DNA, while they have mitochondria, don’t hold on to it.  Remember, mitochondria are energy producers.  It is a long trip up the vagina, through the uterus and into the fallopian tubes to meet that large, slow-moving egg.  What is more, every sperm that makes that trip is in the race of its life.  Only one guy gets to fertilize the egg, so it is “damn the torpedoes; full speed ahead!”  By the time those relentless tail-waggers have made that trip, their mitochondria are too tired to carry on.  They are left behind, outside the wall of the ovum.  To borrow the words of geneticist Stephen Oppenheimer, the men check their guns at the door.

            As with all DNA, the mtDNA can occasionally be changed (mutated) due to myriad environmental factors.  About once every thousand generations, a single letter in the DNA code might be changed.  Once changed, this point mutation is permanent and passed down to every female in the line from that time forward.  This is how female line inheritance can be mapped back through eons of time. 

            So where is this leading?  Check back in a few days and keep the faith.