|Cats Are Not Peas: A Calico History of Genetics|
|by Laura Gould|
Posted: October 20, 2000
But as little as I care for cats, I do love good writing, and I love to spend time with a curious and clever narrator who travels from point A to point B in the most discursive, meandering, and ultimately enlightening way possible. Which is why I found Cats Are Not Peasdespite the unspoken and quite debatable premise that what cats are is inherently lovableso much fun to read.
Gould undertakes the writing of this book, first published in 1996 (and still available in hardback), when she comes into possession of George, one of two cats she picks up at a local animal shelter. Both cats are quite beautiful: George is a calico with long white legs and a white chest and face, and his companion, Max, is a silky, long-haired tom, coal black except for a white tuxedo front. But George is more than just beautiful; he is, according to cat lore, an impossibility. He is a calico and he is male, and calico cats are supposed to be female.
To try to figure out how George came to be, Gould sets out on a scientific quest for which she is only modestly prepared. Her professional background is in computational linguistics, but now she immerses herself in a full-fledged investigation of genetics. She begins in the nineteenth century with Gregor Mendel, a shadowy figure she remembers only vaguely from high school biology. She cogently describes Mendel's work with pea plants (hence the book's title), which he grew for seven years in the garden of his monastery, and explains how "his round and wrinkled peas were to lay the foundation on which modern genetics rests comfortably to this very day."
Then she follows the century-long arc of the history of geneticsgoing off on tangents whenever she possibly can. When she picks up an obscure 1881 book called The Cat, for example, she learns that male calicos were "not unfrequently" offered for sale to the London Zoo for "very extravagant prices." Intrigued, she tries to lay her hands on one of those soliciting lettersonly to be told that the zoo's records were destroyed in World War II. This causes her, in a typical and almost wholly irrelevant digression, to reflect for a few moments on war: "It was a sad reminder of the periodic, catastrophic discontinuities of history that the violence of our speciesand sometimes of natureproduces."
If you like this kind of musing in the middle of your popular science, you will be charmed by Laura Gould; if not, or if you're in a rush to have her get to the POINT already, you might find her a bit irritating.
I, for one, was charmed. I enjoyed entering the world of cat breeding, cat mythology, and "cat fancy" magazines; I liked getting sidetracked by obstreperous university librarians and earthquake-weakened moveable stacks; I evenand this is a big admissionenjoyed the antics of George and Max, sabotaging the cat door in the laundry room, discovering snow for the first time, going on what must have been ridiculous-looking nightly walks with Gould and her husband, and occasionally disappearing for days into the northern California woods.
I was surprised to learn how many genetic investigations involved cats: one scientist, for instanceknown here simply as Mrs. Bisbeewrote in 1927 that "some of the most interesting problems in Genetics are connected with the inheritance of the black, yellow and tortoiseshell coat-colour amongst cats." And I was pleased to pick up some obscure bits of genetics arcana, like the fact that until as recently as 1956 scientists believed the human genome was made of 48 chromosomes rather than 46.
As for the male calico in question, Gould had to look to the X chromosome, where the cat's gene for coat color resides. A cat, she tells us, can have either the "O" gene, for orange, or the "o" gene for black (or, strictly speaking, non-orange). Orange in this case is only partially dominant over non-orange, and a hybrid, "Oo," has a coat with a little bit of orange, a little blackin other words, calico. And since the color gene is on the X chromosome, you can't have a male hybrid, any more than you can have a male carrier of sex-linked diseases like hemophilia, because males have only a single X.
Except, that is, for cats like George. George, it turns out, has the feline version of Klinefelter syndrome, a genetic anomaly that strikes an estimated one in 500 baby boys and is caused by trisomy of the sex chromosomes, leading to the genotype XXY. Although the Y chromosome makes George male, that extra X gives him as many loci as a female would have for the coat color gene. This means he can indeed be a color hybrid, with "O" on one of his X chromosomes and "o" on the other. To someone in the knowas readers of this book are by nowGeorge's calico coat announces his hybrid status, and his hybrid status announces that he must have at least one more X than does a typical male.
One less obvious fact about George, however, is that he isn't a straight XXY. His true karyotype is XXY/XY, which makes him a genetic mosaic. Klinefelter himself documented dozens of such mosaics, in whom not every cell contained exactly the same arrangement of chromosomes. Among them were such bizarre combinations as XXY/XXXY, XXXY/XXXXY, XX/XXXY/XXY, and X0/XY/XXY. In George's case, only half his cells are the standard Klinefelter XXY. The other half, it turns out, are just ordinary male XY.
"So George isn't a new and wonderful type," his indulgent owner concludes. "He's just another boring old XY/XXY, five of which have already been reported in the literature." But watching her beautiful old cat curled up at her feet as she writes, Gould concludes that it's "just as well that he represents nothing new or original. Then people might be asking for just a little piece of his ear, or a snippet of some more private part, for further, more complex analysis." She would rather, she says, let George go on living his happy, sleepy, catty little life, and move on herself from her romp through self-taught genetics to some entirely new kind of adventure. Maybe some day we'll get to read about that one, too.
Robin Marantz Henig is an author living in New York. Her most recent book is "The Monk in the Garden: The Lost and Found Genius of Gregor Mendel" (Houghton-Mifflin, 2000).