Download CLEFT CHIN (PPT picture #8)

7 Beautiful Mutations: Which Ones Do You Have?
I'm a mutant. You're a mutant, too.
If I wasn’t a writer, I think I’d like to be a genetic researcher. I know, they seem like totally
unrelated fields, but hear me out.
The thing that interests me most in the entire world is why people (or characters) are who they are,
and what makes them tick. And one of the things at the very bottom of what makes people tick is in
their genes, and I think that’s why I find genetics so interesting. I love picking out the features that
I inherited from my parents (my dad’s eyes, my mum’s cheekbones) as well as those that haven’t
appeared for several generations (my hair texture).
Since humans are around 99.9% genetically identical, it’s amazing to think that such a tiny
percentage difference can result in such incredible variation in our species. And one of the vehicles
for that variation is genetic mutation.
Unfortunately, we’re not yet mutating the power of flight or telepathy--sorry, Doctor X. A mutation
is a permanent change in the DNA structure of a gene. They can be inherited or acquired, and they
can be beneficial, neutral or pathogenic (seldom are they superpowers). Some mutations eventually
become so common that they’re considered “normal,” whereas others remain rare and unusual in
the human population.
HETEROCHROMIA (PPT picture #1)
I never thought much about my eyes growing up. They were very much like my dad’s, and I figured
that having blue, yellow and green all mixed up together was just what green eyes looked like.
Plus the splodge of brown at the top of my right eye which I call The Blotch. Imagine my surprise to
find out that this is actually quite atypical, and all thanks to a mutation called heterochromia
iridum. It refers to eyes that have multiple colors in them, and you’ve probably heard of it if you’ve
seen X Men: First Class; young Professor X calls it “a very groovy mutation.” (PPT picture #2)
There are three types of heterochromia:
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Complete (each eye a different color).
Sectoral (a segment of contrasting color in the iris).
Central (a different color radiating out from the pupil).
(PPT picture #3)
If you’re born with heterochromia, it’s probably because one of your parents had it--it’s a dominant
trait. It’s also possible to acquire heterochromia, although you probably don’t want to. It’s almost
always the result of a serious illness or injury. Certain medications have been known to deposit
brown pigment in eyes--a pretty rare side-effect, and one that usually only happens in hazel eyes,
but certainly one worth mentioning.
(PPT picture #4)
Most sources I consulted say that heterochromia is super-rare, but from my very scientific study of
xoVainers (both readers and writers), I’ve determined that it really ISN’T rare at all. It seems like
most of us have some form of this, with central being the most popular. Multicoloured eyes unite!
(PPT picture #5)
DOUBLE EYELASHES
It’s called distichiasis, and if you’re born with it, it’s because one of your parents had it (it’s a
dominant trait, so you’re welcome, future offspring). It’s the result of a mutation on your 16th
chromosome, and can also be a symptom of some pretty serious heart-related disorders.
This is another fun mutation expressed in my phenotype. It’s not as obvious on me as it is on
some people, because my eyelashes are blonde. But man, do I ever have a lot of them. There is a
difference, though, between having “lots of eyelashes” and a double row, and it can difficult to
figure out if you have this particular mutation or not.
(PPT picture #6)
Here’s how you can tell: Lift up the lashes on your upper eyelid and peek underneath where the
waterline is. If your eyelashes stop and then your waterline starts, you have beautiful thick lashes.
If, however, you can see lashes sprouting out of your waterline where they should not be (I find this
incredibly distressing), then congratulations, you have distichiasis.
Anecdotally, this isn’t always the super-gorgeous advantage that it sounds like. I had to have seven
eyelashes that were growing in towards my eye removed when I was a kid, which, thankfully, I only
have vague memories of now.
RED HAIR
I think most people know that red hair is a recessive trait; meaning that if you’re a ginger (term
used with lots of love), you have two variant copies of a gene called MC1R on each of your 16th
chromosomes. This mutation results in generally fairer skin, freckles (we’ll get to them), lightcolored eyes, issues dealing with UV light and, recent studies have suggested, a unique pain
tolerance.
That’s all pretty neat, but I want to talk about a totally false idea that regains popularity every
couple of years: that redheads are going extinct, and that there will be no more gingers as early as
2060. No. Just no.
How Stuff Works debunked this very, very thoroughly: “Recessive genes can become rare but
don't disappear completely unless everyone carrying that gene dies or fails to reproduce. So while
red hair may remain rare, enough people carry the gene that, barring global catastrophe, redheads
should continue to appear for some time.”
FRECKLES
I have a few freckles, and I think they are the cutest. I always wished that I had more, probably
because a lot of my friends growing up had them.
And guess what causes them? Or rather, guess what partially causes them? That’s right:
MUTATIONS.
And it all has to do with cells in the skin that make a pigment called melanocytes. When exposed to
UV light, melanocytes produce melanin, which makes skin darker to protect our DNA. There are
two main types of melanin. The second type (Pheomelanin) is less common, and it’s what gives red
hair and freckles their orangey tone.
Remember a second ago when we were talking about red hair and the MC1R gene? That guy is
coming back into play again here. When the MC1R gene is working normally, it turns all the second
type into the first type. This means skin tans instead of freckles, and hair is a colour other than red.
But when the MC1R gene isn’t working, you get red hair and freckled skin thanks to all that lovely
pheomelanin (Type 2 melanin) floating around.
“But Alle,” I hear you saying. “Not all people who have freckles also have red hair.”
You’re so right! Remember how we know that being a ginger is a recessive trait that needs two
copies of a gene--one from each parent--to be expressed? (PPT picture #7)
Amy Pond has red hair. This means she has two copies of the recessive gene. Rory Pond doesn't
have red hair. He has two copies of the "normal" MC1R gene. River Song is their daughter, and
inherits one gene from each. The non-redhead dominant version drowns out the redhead version,
and so River has non-red hair. WHOVIANS, ARE YOU NOT ENTERTAINED?
MCR1 is that gene! Some people have a single mutated copy of it and have no idea--but it means
that not all their Type 2 turns into Type 1 melanin, and they still get freckles when exposed to UV
light. My family hasn’t ever had any redheads in it--we’re generally either dark blondes or have
black Irish hair--but I, and a few of my cousins, still have freckles. It could be that we’re carrying a
single redhead gene, makin’ pheomelanin like it’s our JOBS.
Or it could be something else entirely, because this only applies SOMETIMES. Not all people with
red hair have freckles (though it’s more likely) and, as we know, not all people with freckles also
have red hair. Something else is afoot, but scientists don’t know what it is yet. Another gene doing
something? Environment? No idea!
This is a super-weird result, because it tells us that freckles are a dominant trait, being expressed
even when there’s only one copy of the gene in question, but red hair itself is recessive-even though they’re both caused by the same gene. Genetics is really cool and complicated, guys.
BLUE EYES
I know: WHAAAAAAAA? Blue eyes aren’t exactly rare! But mutations don’t have to be rare--this
one now appears in so much of the population that it's considered a polymorph. But really, blue
eyes are the result of a pretty recent mutation. You know, 10,000 years ago. Practically yesterday.
The first thing you have to know is that blue eyes aren’t technically a color--they’re a lack of
color. Eye color is determined by pigments in a part of the iris, and if there is a tiny amount of
pigment there (or none at all), eyes will appear blue. A bit more pigment gives us green eyes. And if
there’s heaps of pigment, eyes are brown.
The gene that’s responsible for this is called OCA2, and it controls melanin. Back in the day, all
humans had brown eyes--eyes with lots of melanin pigment. One day, a nearby gene mutated and
started to limit OCA2’s ability to produce melanin in the iris. This stopped melanin from coloring
the eyes, leaving the iris blue, and voila! Blue eyes appeared in the population.
In fact, scientists currently think that everyone who has blue eyes is descended from a single
common ancestor who lived around the Black Sea six to ten thousand years ago. How’s that for
neat?
CLEFT CHIN (PPT picture #8)
Cleft chins are caused when the two halves of the jaw bone (or muscle) don’t quite fuse properly
during development. Common wisdom states that this is a primarily dominant genetic trait. Allow
me to bust this myth.
First: not all cleft chins are exactly the same. There’s heaps of variation when it comes to size and
depth (very subtle vs very deep). So it’s sometimes harder than you’d think to say which chin is
smooth and which isn’t.
Second: men are more frequently cleft-chinned than women are which doesn’t fit the simple
dominant-recessive patterns. A really old study (from 1939) recorded that 9.6% of German men
and 4.5% of German women had cleft chins. That’s a really big difference between sexes for a trait
that isn’t supposed to be sex-linked.
Another study (from 1960) found that even when two parents had smooth chins, they could still
have cleft-chinned offspring. It didn’t happen often (11% of the time), but it happened. If cleft chins
truly are dominant, this should have been impossible. Another genetic mystery waiting to be
solved!
NO-SHOW WISDOM TEETH (PPT picture #9)
If there's one thing I wish would just DIE RIGHT OUT OF THE HUMAN POPULATION, it would
be wisdom teeth. Mine popped up when I was 20, all four completely on their sides, two of them
poking through the gums like painful little islands in a sea of pink gum.
When I cursed my horrible teeth to my dad, he got really quiet and said “I never had those.” Yep.
My dad is one of the lucky ones who were born without wisdom teeth. (note-so was Ms. Davis!)
As things are right now, we aren’t totally sure that this is a mutation, because we’re not sure why
wisdom teeth don’t show up (even though it happens in an estimated 35% of the population). Is
there a gene that says “NO, WISDOM TEETH, DO NOT GROW HERE”? A bunch of genes? Is it
due to environmental factors? Some kind of physical injury in childhood that prevents them from
forming? Nobody knows for sure! (note-Ms. Davis never had any physical injury to her mouth, just
sayin’.)
There’s some recent evidence that the suppression of wisdom teeth was a mutation that popped up
in China three to four hundred THOUSAND years ago. This doesn’t prove anything, but it sure is
interesting to think that my dad is possibly the beneficiary of a four-hundred-thousand-year-old
mutation. Although if the point of variation like this is to pass them down to your children, that
didn’t work out very well. Both my brother and I had fully impacted wisdom teeth followed by
painful surgeries and long recoveries.