Does your mother drive you crazy? Is the thought that you might be turning into a younger, slightly hipper version of her keeping you awake at night? Do you want to scream when she advises you on (choose one) your love life? Your marriage? Your children? Or, are you just the opposite? Your mother is one of your dearest friends and confidants. You're as close as sisters, as alike as two peas in a pod. You call her three times a week just to get her opinion on your (choose one) love life, marriage, children. Maybe you fall into another category altogether. You're estranged from your mother, or she's deceased, or she's just plain gone, maybe physically, maybe into a bottle. Maybe you don't even know who she is, much less where she is, and you're happier that way, better off. Whatever your circumstances, Mother's Day comes for all of us, a day so fraught with emotion, guilt, ambivalence, and expectation that it's hard to believe that it was dreamed up by a greeting card company as a way to generate profits. You'd think that a much higher authority than Hallmark would have ordained something so powerful as Mother's Day.

I'm no expert on mother-daughter relations, having had a very skewed experience of them. Separated from my mother shortly after my thirteenth birthday, raised through adolescence by my grandmother, I sometimes feel like a clumsy extraterrestrial when it comes to matters of mothering. The idea of hating my mother, or thinking her freakish, stupid, lumpy, is completely alien to me. I adored my mother - as far as I was concerned, she was the smartest, coolest, prettiest mom a person could have. I adored my grandmother too, and found her funny and inspirational and filled with joy. That whole teenage girl rebellion thing? I missed it completely. Not because I was some kind of wonderful kid, but because my mother was gone from me at precisely the time when I would have started to push her away. Since any proper uprising requires a tyrant, my mutiny ended before it could begin. I've known a few other women who grew up in circumstances similar to mine, and while we all made mistakes - big ones sometimes - none of us enjoyed the luxury of a classic mother-daughter rebellion. And make no mistake: rebellion is a luxury. It's an opportunity to test and measure the very shape and contours of your identity, to discover both who you are and who you are not, in an environment of perfect safety. This safety comes not from the world, which is a treacherous and sometimes deadly place for an adolescent girl, but from the unconditional love of a parent. You may be blind to it at the time, you may be raging, pulling, struggling, but it's there all the same: I am your mother, and you are my child. Nothing you do or say can change that.

Now it turns out that mothers and daughters share another common bond, one powerful enough to carry across continents and centuries. Inside every human cell, there are tiny engines known as mitochondria. Each has it's own DNA. There are mitochondria in both eggs and sperm but when an embryo is fertilized, only the mother's mitochondria remain and multiply. This particular DNA is known as mtDNA, and is passed intact, unchanged, to offspring. Both daughters and sons receive the mother's mtDNA, but since it can only be passed along in eggs, sons cannot pass it to their children. The theory is that every daughter carries the identical mtDNA as her mother, and her mother's mother, and her mother's mother, and so on, all the way back in time to an original female ancestor. (The male equivalent is the Y chromosome, which, unless it undergoes a rare mutation, is passed essentially unchanged down through the male line of a family.) There are a lot of interesting applications for this research, not the least being its usefulness in establishing paternity or accurate genealogical profiles. The science of genetics fascinating, but so is the poetry of it. Imagine all of the unknown women it took to bring you to this moment, to create you, to make you possible. How many of us can trace our ancestry back more than a few generations? In my case, I'm the granddaughter of immigrants, poor peasants who came to this country all but illiterate, with no grand history of royalty or scholarship. Their stories are lost to me, forgotten in their tiny villages in Europe. My father's mother's mother came from Italy, her people dead, their family traditions left behind. My mother's mother came to America from Northern Ireland as an orphan. What can be known, what was recorded about the lives of these poor working people who struggled day to day for survival? When I peer backward, looking for the women whose mtDNA I share, I can't see any further than a great-grandmother - all the rest are lost to the inky blackness of history. To think that we share something so fundamental, to know that I carry in every one of my cells a piece of them, thrills me. I feel connected to something so much larger than I'd ever imagined. To be the daughter of females strong enough to propel their genes thousands of years into the future makes me feel powerful and empowered. Yet I exist only because my matrilineal ancestors successfully dodged predators, disease, the hazards of childbirth, hunger, drought, and the countless other perils that would have taken them - and me - out of the gene pool permanently. I also think: I am my mother's only daughter. Unless I have a daughter of my own, I won't pass our unique mtDNA along. After untold generations, our mother-daughter genetic story will end with me. And I can only speculate on how it might feel to have never known your biological mother. Would it be exciting to discover that you are a link in a long, unbroken genetic chain? Or would it be just one more unanswered question to puzzle over?

However you define it, being a mother is hard work. Even the very best candidates for the job don't always get it right. Television has made it even tougher by giving us role models so saccharine, organized and understanding that no real woman could ever hope to compete. Sure, Carol Brady never lost her temper - but she had a live-in maid and a ridiculously agreeable brood of kids on her side. Neither June Cleaver nor Donna Reed ever dealt with projectile vomiting, high school keg parties, or ADHD. The mom on "Seventh Heaven"? She births a kid about every two years, yet still manages to learn piano, origami, feng shui, and gourmet cooking - all while never letting her blonde highlights grow out. Real moms lose their tempers, and sometimes their waistlines. Their roots show. Their cars are dirty. Their purses and houses and minds are often chaotic and jumbled. You don't have to be a mom yourself to appreciate how challenging the job is - ask your own mother. Or a friend, a neighbor, a coworker. It can be a nasty, heartbreaking, thankless job. One of the rewards of motherhood though, is to be remembered and acknowledged on that special Sunday in May. So this Mother's Day, perhaps you might go a step beyond the overpriced greeting card that never truly manages to convey what's in your heart. Send the flowers or the potted plant, but don't stop there. Close your eyes and try to imagine yourself, linked hand-in-hand, with all of the mothers who came before made you possible. Feel proud to be part of that story. Know that it continues with you, and in you, in every cell of your body. That's pretty cool, no matter what kind of mother you've had - or are. Happy Mother's Day.