Foiled by Andrea Barrett

My favorite of the Andrea Barrett stories that we read from Ship Fever is “The Behavior of the Hawkweeds.” I love the intricacy of it, the details – even knowing all along that it’s a work of fiction, I could have sworn that the story must have happened. It’s just so well written.

So, while sitting in my Bio 100 lecture on Genetics last week, I was surprised when my professor mentioned that polydactyly is dominant. In Barrett’s story, the husband of Antonia, the protagonist, was born with an extra finger. While the couple has two normal daughters – each with 10 fingers and 10 toes – one of these daughters bears a son with “six toes on each foot.”

I thought I had caught Barrett out. In my (limited) understanding of genetics, a dominant trait can’t skip a generation, only a recessive trait can; that is, if Antonia’s grandson was a polydactyl, Antonia’s daughter who gave birth to the son must have been a polydactyl, too.

And then I was reminded just how limited my understanding of genetics actually is. I approached my professor on Monday after lecture to ask him whether Barrett had, in fact, made a mistake. As it happens, by some sneaky means meant to confuse falsely-triumphant English majors, other genes can mask a trait, even if that trait is dominant. When searching the Internet for more details, I was unable to find out more information – for example, how likely this is to happen.

Regardless, I think Andrea Barrett wins this round.

-Michelle C.

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~ by Michelle Cohen on March 4, 2010.

2 Responses to “Foiled by Andrea Barrett”

  1. As a student taking Principles of Genetics this semester, I have also heard of this concept in class. There are differences in what is termed “penetrance,” a term referring to the likelihood that the gene will generate any phenotype at all. According to wikipedia (if you dare trust it as an authority source), variability in penetrance can be determined by environmental modifiers, genetic modifiers, epigenetic regulation, or even age. As for the answer your question, polydactyl is 90% penetrant, as seen by a 1984 study referenced below.

    Science is tricky, as there are always exceptions to every rule; finding info online is increasingly difficult. For me, there’s no way I would have known about it if it wasn’t something that was pounded into my head in class.

    http://books.google.com/books?id=8-40zb0VoRAC&pg=PA397&lpg=PA397&dq=penetrance+of+polydactyl&source=bl&ots=ni41iuPF2X&sig=j-6i3zpLa1ZtilP51P5KoGXcbzI&hl=en&ei=7iuPS8rWI4S1tgfD2pGVCw&sa=X&oi=book_result&ct=result&resnum=5&ved=0CBcQ6AEwBA

    • Thanks for your comment – it was really helpful! Your link gives a really good explanation, and just knowing the word penetrance helped my searches a lot.

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