Genetic math: Is Ben Stiller his parents? Or his own damn self?

15 Nov
Ben Stiller

Ben Stiller. Creative Commons photo by Jerry Avenaim

How much of me is me?  Am I “destined” to become my mom?  Why do I “see myself” in my dad’s parents’ photographs, circa 1951, and not my mom’s?

There’s a saying that applies to all of us:

“Mirror, mirror, on the wall, I am my mother after all.”

But mirror, mirror, to be true, I’m half my mom and half dad, too.

And nature adds to her Great Tree a teensy dash of Only Me.

As we now discuss the proportional contributions of our genetic forebears, note that we are setting aside the countless, profoundly significant things that make us who we are that have nothing to do with cellular biology.  And, to be honest, we are even setting aside many aspects of cellular biology that make up our humanness but are not orchestrated by genes.  People are more than genetic casseroles.

Nonetheless we are endlessly and justifiably curious about the ingredients of the casseroles that are our genetic selves. And so for a brief, educational minute, let us contemplate the essence of Ben Stiller.

Half mom, half dad

Exactly half of Ben Stiller’s genes came from the comedian Anne Meara, and the other half came from the comedian Jerry Stiller.  (In a “Funny or Die” Web sketch, Ben Stiller marches out of an interview after host Zach Galafianakis asks him: “Do you ever wish you had followed your parents into comedy?”)

Inside of almost all of Ben Stiller’s cells are 3 billion Anne Meara DNA base pairs and 3 billion Jerry Stiller base pairs, give or take.

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Trace Ben Stiller’s genes back through previous generations, though, and the math gets more complicated.

Diluted ancestors

In all likelihood Ben Stiller has about a quarter of each of his grandparents’ genes, but this split isn’t necessarily even.

The egg that made Ben Stiller contained chromosomes that were an unpredictable mosaic of Anne Meara’s parents.  The sperm that made Ben Stiller contained chromosomes that were an unpredictable mix of Jerry Stiller’s parents.

This is true because of meiosis, the chromosomal square dance that puts unique combinations of chromosomes into sperm and egg cells.

But there is even more wildness on this dance floor than just the movement of chromosomal ladies and gents into their corners.  Through a fascinating process called “crossing over,” each chromosomal pair we inherited from our parents lines up like the Virginia Reel and exchanges a large part of its own self (that is, a chromosome arm or a leg) with the lady or gent chromosome standing opposite.  At the end of that prophase moment, there are a lot of recombined (you might even say “cross-dressing”) partners left for the rest of the meiosis dance into individual eggs or sperm.

In the end, Ben Stiller has a set of 23 chromosomes from his mom and another set from his dad, but each of these 46 chromomomes represents a unique blend of Ben Stiller’s grandparents.

As a brief aside, let’s unpack that statement by imagining that over the actor’s fireplace hangs an oil portrait of Stiller’s two largest chromosomes.  There they stand: Meara Chromosome 1 on the left and J. Stiller Chromosome 1 on the right, like two august worms.

The artist painted in pink the areas of each chromosome that Stiller took from his grandmothers, and blue the areas he got from his grandfathers.  Where did he apply each color, and in what quantity?  Here the artist could only guess.  Whether Ben Stiller’s chromosomes 1 through 22 (leaving out the sex chromosome) are “pink” or “blue,” or splotched or not at each end with the opposite color is one of nature’s tricks of chance, and this is why genes among siblings are endlessly varied.

The proportions, then, of Ben Stiller’s grandparents in the recipe for cooking up a Ben Stiller casserole, are unknown.  Most likely Ben Stiller “is” about a quarter of each of his grandparents, an eighth of each of his great-grandparents, a sixteenth of his great-greats, and so on, but since the fraction could be more or less in each case, Ben Stiller could have a direct ancestor many generations back whose genetic contribution to him is zero.

Personal mutations

Yet another complication in the math of our genetic inheritance is personal, or private mutation.

It’s not like they are secret or hidden, but because they probably have not been seen on the planet before (or at least very rarely), they are called “private” mutations rather than common mutations (like blood types A, B, AB and O).

Yet another complication in the math of our genetic inheritance is personal, “private” mutations. It’s not like they are secret or hidden, but because they probably have not been seen on the planet before (or at least very rarely), they are called “private” mutations rather than common mutations (like blood types A, B, AB, and O).

Mutations can have long or short histories.  Common mutations like attached earlobes go back thousands of generations.  All human populations have these common mutations that brought us our uniquely human features, capabilities and adaptations, as, for example, our opposable thumbs.  Other mutations are unique within a family.

Ben Stiller has about 100 mutations that are unique to him.  He also inherited about 50, or half, of the mutations that had been unique to his mother, and another 50 from his father, and he would have passed half of those, or 25 from each, to his children[tmp1] .

In total, Ben Stiller has in his chromosomes about 6 billion base pairs, of which 3 million are mutations commonly found around the globe and from the countries where his ancestors came from and multiplied.  On top of that, roughly 100 mutations came about when the egg and sperm that made him were first created.  Those 100 mutations then got copied along with all the other DNA in all of Ben Stiller’s cells as he developed in utero.  These mutations perhaps had never been on the planet before and may never be again— or, 50 percent of them may have been passed on to Ben Stiller’s kids, Ella and Quinlin.  These children, in turn, have mutations that are unique to them.

How did this happen? Well, Anne Meara and Jerry Stiller each have 46 chromosomes that comprise a code that is 6 billion letters long.  Before an egg (in Anne) or a sperm (in Jerry) could be created, an entire copy of that code had to be written out.  Hundreds of little DNA polymerases do the work of “hand-copying” the genome, and they do it in about an hour.  (These DNA polymerases are fast, pretty accurate replicators of DNA that we make ourselves.  The gene for making polymerases is found within our chromosomes.)  Given the enormity of the original, it is amazing that the copy typically ends up with about 100 “typographical errors,” or mutations, in each of us.

But even that’s not the whole story because the single cell that became Ben Stiller went through trillions of replications and then cell divisions.  And they continue to replicate, since after all the skin and hair cells Ben Stiller had in “There’s Something about Mary” were not the same skin and hair cells he had in “Zoolander.”

Every time the cell gets ready to divide and makes a whole brand-new copy of its chromosomes, stuff happens. There are little mutations, rearrangements or insertions that occur as the genome is transcribed, many of which are proofread and corrected, but “somatic mutation” is the term we give to all the variability that accumulates in all the cell lineages in the body, and something on the order of 80 percent of all cancer is associated with these somatic mutations.

Photo from Ben Stiller tweet, "Guess who sunburn leg?"

UV rays, for example, can cause somatic mutations.

That, and this photo to the left, is why Ben Stiller should wear sunscreen.

Genes that are unexpressed

Ben Stiller has some genes that will never be “expressed” during his lifetime, and he also has genetic attributes that nobody will ever notice.

And that’s an OK thing.  Some genes are just “embryo genes,” designed to express themselves very early on, in utero.  Other genes turn “on” and “off” during other stages of development like birth, adolescence, and adulthood.

Some genes never get turned on because a person isn’t exposed to an environment that would trigger them.  Ben Stiller has, for example, sort of “lifeboat” genes called cold shock and heat shock genes that could help him handle Arctic temperatures or a high fever.  He also has genes for metabolizing alcohol, so if he teetotals those genes will never be called on to be expressed.

Some genes are just not that impressive

Any of Ben Stiller’s attributes that are genetically determined almost always represent a mix of genes passed along to him by Anne Meara and Jerry Stiller.  Even if we all agree that Ben Stiller has “his father’s eyes,” Anne Meara inevitably contributed.  What we are cuing into is likely a Stillerian genetic mutation that is dominant.

Zebra finch. Creative Commons photo by Maurice van Bruggen

As humans we notice things like eyes, and smiles, and body shape, while there are other genetic attributes that we just aren’t keyed into.  In another universe we might say of Ben Stiller that he is a man of  lumpy liver and ruggedly handsome pancreas.  If we communicated in the way that musicals pretend that we do, we perhaps might be able to hear Stiller’s genetic legacy in the timbre of his voice.  A zebra finch would more likely notice Ben Stiller’s vocal patterns than the hollows in his cheeks.  After all, a finch’s whole world is song.


2 Responses to “Genetic math: Is Ben Stiller his parents? Or his own damn self?”

  1. Ginny June 15, 2011 at 4:52 pm #

    LOVE the way you make a serious, sometimes complicated process easier to understand AND, at the same time, fun and personal (or maybe it’s because it’s fun and personal that it’s easier to understand… Keep writing!

  2. Ant June 16, 2011 at 12:34 am #

    Insightful stuff.

    Makes me chuckle as I think of times when mother would sigh and say “Ugh .. you’re just like your father”.
    Of course, I know I’m not EXACTLY like my father.

    Can we explore Megan Fox for the next blog entry?? =)

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