Before I began studying for the MCAT biology section this month, the only kind of pedigree I knew about was the sort that my dogs (below) don't have.
we can't all be perfect
My opinion on that sort of pedigree was as follows: if you'd rather own a purebred dog whose original ancestors were most likely a troll and a floor mop, you can take your pedigree and shove it.
sorry, baby chewbacca: the truth hurts
Having been a metaphorically rabid canine lover my entire life, I thought I knew everything there was to know about pedigree. I could identify rare dog breeds on site. I could quote entire scenes from Best in Show. And every year I dutifully watched the major dog shows and prayed my unanswered prayer: oh dear God who art in heaven, please rain mercy upon us and for the love of all that is good and holy, let a not-hideous dog win.
I was convinced beyond a shadow of a doubt that I had pedigree down pat. Cue the MCAT.
I say whaaaaa
Pedigree charts, I am learning, are the bread and butter of the MCAT kitchen. In fact, it's hard to tell which the MCAT loves more: pedigree charts or hemoglobin. I'm not exactly sure what a pedigree chart ever did to deserve this fame. It was just moseying along, doing its thing, telling people that they had a 50% likelihood of developing early-onset Alzheimer's, when suddenly its face appeared on every major version of the most important standardized test in the nation. And it liked it. It wanted more. And within a matter of months, the pedigree chart became the Regina George of MCAT High.
regina, you are an empty circle on the pedigree chart of my heart
But! You say. Celeste, is it really that complicated? A pedigree chart should be the least of your problems. Aren't you making a mountain out of a molehill? Aren't you putting words in my mouth? And I would say yes no yes. What seems like a simple concept: represent a bunch of generations with some lines and squares and circles, then answer a question like the following, nicked from my Kaplan review book. . .
52. A form of MODY called atypical diabetic mellitus (ADM), which has been identified only in African-American and some Asian populations, is characterized by initial need for insulin that eventually gives way to type II diabetic symptoms. If individual III-17 was to marry a heterozygote for ADM, what is the likelihood that their child would inherit a permanently insulin-dependent form of diabetes?
A. 0%
B. 25%
C. 50%
D. 100%
E. Paula Deen
. . .isn't so simple after all. This is mostly because I am an idiot, refusing to remember/relearn pedigree chart notation, than because pedigree charts are actually difficult. So, reluctantly, let's break it all down:
1. If you are in possession of a penis, you are a square. If you have a vagina, you are a circle. If you identify as genderless, please stop making trouble.
Why women were chosen to be represented by a soft, round, friendly shape, while men were paired with a sharp, angular one is a dissertation just waiting to happen. Regardless, it is helpful to remember this distinction, as the MCAT seems obsessed with tricking you into thinking a disease is all cute and autosomal, when actually it's . . .wait for it. . .sex-linked. Or even worse: passed through the mother's mitochondrial DNA. MCAT, you really hit me where it hurts.
2. If a man and a woman love each other very much and have made an everlasting commitment to stay together in sickness and in health (and there will definitely be some sickness), they will make little square and circle babies who will be connected to them by a line.
I imagine this to be sort of like those mothers who drag their toddlers around the mall on leashes. Except this time you're in a mall the size of the universe and you're tied to your children forever and ever. Which is to say, if you are on a pedigree chart and you have children, there is no empty-nesting or secret adoptions. No. You have 5 kids, two of which are carriers for sickle cell anemia and everyone knows you have 5 kids, two of which are carriers for sickle cell anemia. Put Jerry Springer out of business, why don't you.
3. If you are six feet under, there will be a little slash through your circle or square body.
Sorry, John Donne: the poetry stops here. Expect neither flowers nor hymns, friends--when you kick the bucket on a pedigree chart you are simply sliced through with a little line of ink.
4. If you are white, you are healthy. If you are half-white, you are probably carrying a DNA time bomb. If you are black, you're screwed.
Again, a dissertation waiting to happen. (Squares of Injustice, Circles of Hate: An Analysis of Race and Representation in Medical Pedigree Charts Of the 20th Century.) You'd think this black/not black system would make everything crystal-clear, but half the time the MCAT doesn't even tell you what disease the family has. You know some people are in trouble, but you don't immediately know how. Which is like being a real doctor, I suppose. (MCAT: y u so smart??)
5. We don't talk about incest and divorce.
Put aside your emotional devastation about the above subjects, and imagine for a second how messy a pedigree chart would be of the Real Housewives of Orange County ("I'm sorry, ladies, for some reason you're all coming up as orange circles?") We just can't have that kind of riff-raff messing up our science. Too many lines. Too many generations. Let's all just stay together for the pre-med kids.
*
And that's that. Even though we are now fully informed on the ins and outs of pedigree charts, I think all of us can agree--purebred and mutt alike--that still. . .
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