TRYING TO UNDERSTAND human genetics, it’s best to think in terms of distance, or how genetically far we are from one another. When it was proposed that we are related to chimps, the Victorians went wild, in part because they saw the distance between us and monkeys to be a lot closer than it is. A little knowledge later, and we’re all a lot more comfortable with being part of an evolving continuum, hairy as some of those stops along the road may be. So, who’s the closest of them all? Here’s a hint: She’s even closer than you think.
Maybe you look as little like your sister as do Margaret and Marion, TSP’s “She Said, She Said” bloggers. Small-boned, thin, brown-haired with blue eyes, Margaret seems a world away from her younger sister who, built on a much larger frame, is red-haired with hazel eyes. How we map out genetically, called our genotype, is expressed in part in how we look–known as our phenotype–though the genotype also carries within it all those things that we inherit but are not expressed.
This is why red hair, well known to appear in one generation and not the next, may pop up again later in many families. And while one or a few genes determine each trait, there are more than 25,000 genes in each human body and each one travels with its alternate. These alternate pairs are called alleles, and in total, represent all the possibilities imaginable.
And if that’s not a big enough menu for you, where you grow up, what you eat and what you do are the environmental–as opposed to genetic–factors, which have their say, as well. Reduced to a punchy headline, this is the Nature Versus Nurture Debate, making us genetically nearly the same, while allowing for human choice, free will, as well as random occurrences to spice things up, making us both appear and perhaps behave as distinctly ourselves.
However, your DNA sequence is pretty much 99.9% identical to any other human. Pretty damn close, wouldn’t you say? Well, maybe not.
The closest people on earth to you genetically are your same-sex siblings. Yes, your sisters. Nobody’s closer.
The map of your chromosomes carries genes, which carry those alleles. Humans have 46 chromosomes, inheriting 22 non-sex chromosomes, and one sex chromosome from each parent, making you 99.95% biochemically identical to your parents. Feeling close? We can get tighter, still. Human sex chromosomes are labeled X and Y (though did you ever see a sex show labeled with a triple Y? I don’t think so), with X for the female sex chromosome, and Y for the male.
Women are XX, getting one X from their mothers and the other from paternal grandmothers. Men are XY, retaining one of his mother’s Xs and getting his Y from his dad. At replication, daughters get one X from their mothers. Their second X comes from Dad–the same one he got from Mom–meaning that while you can inherit either one of your mother’s Xs, your father, having only one X to give, gives the same one to all daughters. In the case of brothers, they all get the Y from Dad.
The result? The closest possible people on earth to you are your siblings, specifically, your same-sex sibling. That’s nature.
Nurture? That’s what The Sisters Project does best, and with 6.7 billion people on earth, 51% of them women, 80 percent of who have sisters, there’s a whole lot of nurturing we can do.–Marion Roach Smith
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Wonderful article. It is crucial to realize, and it is mentioned in this article, that where we grow up has a tremendous amount to do with what type of person we become. If everyone realized this, world peace would possible.
Welcome, Joe. It is a very important factor, indeed. Thanks for your comment, and do visit again soon.
This is bittersweet news, because while I’m genetically closer to my only sister, we are not close. Being that we’ve both hit mid-lfe, she 49 and I a recent 47 (June 1st), is it too late? How do we go about re-writing our previous history? Our family was never one to get “mushy” and share “feelings and emotions.” Fear keeps me from being vulnerable and saying, “I want us to be closer,” but I’m determined to get my nerve up…Sisters, wish me lots of luck and godspeed.
TSP has been a blessing because it has made me realize and articulate how torturing it is to have a sister and not be close. It has also made me realize how important it is to make the effort. As Maya Angelou said, “Courage is the noblest of virtues, for without courage, you cannot live out any of the other virtues consistently.” And as we all know, courage is simply doing it afraid, right ladies?
So very true, Lisa. I do wish you luck and godspeed. It’s only six short words, and chances are 50-50 that she’s wishing she could say them, too. People buy lottery tickets with much lower odds of winning. And what a prize you could have!
Hello, Lisa. We are so glad that TSP is a blessing for you. Yes, courage is simply doing it afraid. Such a great thing to remember, and we’re so glad you bring that up to remind us. Keep coming back, Lisa. We’re here for you.
Hello, Helen, and thanks for stopping by TSP. You’re right, of course, and how sisterly of you to support Lisa in this way. Right on. Please come back soon.