Phenotype, by the way, is a word you have to get used to if you spend any time with biologists, particularly geneticists. It basically means the way the animal appears. If scientists were simply to say, “That strain of mouse has an unusual appearance,” it would not sound half so erudite and educated as when they say, “That mouse has an unusual phenotype.” So scientists generally stick with phenotype.
Phenotype should not be confused with genotype. Genotype refers to the particular set of DNA letters that make up a mouse’s genetic instructions. Often, changing a mouse’s genotype by removing or adding DNA letters will change its phenotype—but not always. A mouse with an interesting phenotype often will also have an interesting genotype. Not always, but often enough that by studying mice with interesting phenotypes, scientists learn interesting things about the genetics of a particular trait.
In the case of Sharkey, the interesting phenotype is that these mice have extra teeth.[2] To show off this dental precociousness, Curtain reaches into the box containing Sharkey mice and picks one up by the tail. She then lowers it so that its forepaws can reach the top of the box. The mouse, sensing a safe haven, grabs onto the lip of the box, and for a brief instant, it becomes a mouse bridge, anchored at one end by its forepaws on the box and at the other by Curtain’s blue latex–gloved hand. This position makes it easy for Curtain to grab the mouse by the scruff of the neck with her free hand and turn it over. She performs these maneuvers smoothly, with a practiced air.
Sure enough, with the mouse’s mouth open, it’s easy to see a few extra small teeth tucked in next to the ones that appear to belong there. The idea in creating Sharkey mice isn’t merely to populate a mouse freak show. Scientists have already begun to unravel the steps in tooth formation by using mutant strains such as Sharkey. Wouldn’t it be nice if someday this research made it possible to grow a new molar, instead of getting a crown on one that you cracked on an olive pit?
Another thing scientists may learn from mice is something about the genetics of annoyance. You see, all mice probably become somewhat annoyed from time to time, but other mice get really annoyed a lot of the time, and the difference is probably genetic. Take the strain known as Fierce. Elizabeth Simpson developed this strain while she was working at the Jackson Laboratory. Now she’s at the University of British Columbia. It’s not hard to see how this strain got its name. A normal mouse, when lifted up by its tail, will just hang there. Oh, it might twist around a bit, but basically, lifting a mouse by its tail is a pretty safe way to grab one. A Fierce mouse, on the other hand, will swing itself up so that it can grab its own tail and then use the tail as a kind of climbing rope so that it can bite the person who dared to pick it up.
You don’t have to pick up these mice to get them riled up. Bump their cages, and they turn into biting terrors. Simpson says the scientists have learned that if they don’t want to chase these mice all over the lab, they must put their boxes in large plastic garbage cans before taking off the lids. Because the minute the tops are lifted off, the mice start bouncing around like popcorn, trying to jump onto and bite the person or the people who jostled their home.
You might say that these mice are easily annoyed. Elizabeth Simpson prefers not to say that. She says that calling a mouse “annoyed” is anthropomorphizing—assigning human feelings or emotions to an animal (or an object)—and that anthropomorphizing “is something scientists try not to do. And we tell our students not to do it.” Really, she says, there’s no way of knowing what annoys a mouse, because we can’t ask them.
As long as that’s clear, for the sake of argument, she’s willing to say that her Fierce mice appear to be easily annoyed. She’s even found a gene that seems to be responsible for this behavior. It’s got a catchy name: NR2E1. This gene seems to play an important role in brain development in mammals, although it’s also found in fruit flies (small brains), roundworms (really, really small brains), and sponges (no brains at all). Without reference to the question of whether sponges can get annoyed, Simpson says mice that are missing the NR2E1 gene exhibit the Fierce phenotype. There’s that word again. In this case, it refers not only to the mouse’s physical appearance but to its behavior as well.
Humans also have a version of NR2E1. In fact, if you put a healthy human NR2E1 gene into a Fierce mouse that’s missing NR2E1, the mouse loses its hyperagressive behavior and turns back into a normal mouse. What happens when the human NR2E1 gene is missing or mutated? Simpson is trying to answer that question. Already she has some hints that the gene might be damaged in patients with bipolar disorder.
Simpson says that the Fierce strain is interesting to study for what it might explain about the genetics of human behavior, but mice of this strain are not easy to study. Not long after Simpson started to breed these mice at the Jackson Laboratory, her lab technician came to her and said, “I quit. I can’t stand working with these mice.”
“I understood what she meant,” Simpson says. “These mice are difficult to handle, difficult to breed, and a pain in the neck to work with. Basically, these mice are incredibly annoying.”
So while it may not be possible to say for sure whether a mouse is annoyed, at least Simpson knows how to make a mouse annoying.
7. The Terror of Perfect Pitch
Sometimes sounds annoy people and it’s not about the sound’s intrinsic characteristics and it’s not about personal taste. It’s about the listener. Certain people have special sensitivities. Remember Linda Bartoshuk and her supertasters? Think of Lucy Fitz Gibbon as a superlistener. As with most superpowers, superlistening sounds like a good thing, unless you’re the one who has to live with it.
Fitz Gibbon received her undergraduate degree at Yale University. She has brown hair and wears brown-framed glasses and seems perfectly easygoing, except when she describes the scanner in her office at the Yale Center for British Art, where she works part time. She calls it her Waterloo. It’s loud. It’s repetitive. It’s often in use. This seems more like a minor annoyance, however, not a disastrous military defeat. Yet when Lucy recalls the tone, which she hums, she can’t help but squint and crumple her brow. “It’s so bad. The pitch that it makes is just flat of a C natural.”
Lucy has perfect pitch and years of musical training—which can be a deadly combination for aural annoyance. Perfect pitch, which researchers call absolute pitch, is classically defined as the ability to identify notes without the use of a reference tone. What it means is that whenever Lucy walks down the street, she hears musical notes in sounds that most people experience as noise. Every buzz, rumble, and honk has a pitch associated with it. “Most objects, if they’re moving—like the fan in your computer or the buzzing in your light bulb—make some sort of overtone,” says Lucy. And most of the time, those notes are not in tune.
A walk in New Haven quickly reveals how differently Lucy experiences the world. A big blue truck idling on High Street: “It’s an E flat.” The crosswalk bell by Yale’s largest dining hall, “Commons,” rings slightly flat of a C natural. “I’m pretty sure that it’s the exact same pitch of the bells in my high school that used to ring to tell you to go to class. The first time I heard it, I had this Pavlovian response, and I was back in high school, thinking, ‘Must get to biology.’” It’s common for people with perfect pitch to have excellent tonal memory as well, researchers say.