Chapter 8. Hormones and Sex
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Sara Reardon As a medical student in Paris in the 1980s, Eric Vilain found himself pondering the differences between men and women. What causes them to develop differently, and what happens when the process goes awry? At the time, he was encountering babies that defied simple classification as a boy or girl. Born with disorders of sex development (DSDs), many had intermediate genitalia — an overlarge clitoris, an undersized penis or features of both sexes. Then, as now, the usual practice was to operate. And the decision of whether a child would be left with male or female genitalia was often made not on scientific evidence, says Vilain, but on practicality: an oft-repeated, if insensitive, line has it that “it's easier to dig a hole than build a pole”. Vilain found the approach disturbing. “I was fascinated and shocked by how the medical team was making decisions.” Vilain has spent the better part of his career studying the ambiguities of sex. Now a paediatrician and geneticist at the University of California, Los Angeles (UCLA), he is one of the world's foremost experts on the genetic determinants of DSDs. He has worked closely with intersex advocacy groups that campaign for recognition and better medical treatment — a movement that has recently gained momentum. And in 2011, he established a major longitudinal study to track the psychological and medical well-being of hundreds of children with DSDs. © 2016 Nature Publishing Group
By David Shultz Did you sleep well? The answer may depend on your age, location and gender. A survey of 5000 sleepers from across the world has revealed that women get the most sleep, particularly those under the age of 25. Daniel Forger at the University of Michigan in Ann Arbor and his team were able to get their huge dataset thanks to Entrain, a smartphone app that people use to track their sleep. With their consent, Forger’s team accessed users’ data on their wake time, bed time, time zone and how much light they were exposed to during the day. Analysing this information, they found that middle-aged men sleep the least, while women under the age of 25 sleep the most. As a whole, women appear to sleep on average for 30 minutes longer than men, thanks to going to bed slightly earlier and waking up slightly later. For an individual, the time they woke up had the strongest link to how much sleep they got, suggesting that having a job that starts early every day can mean that you get less sleep than someone who starts work at a later hour. There were also differences between countries. People in Singapore, for example, sleep for an average of 7.5 hours a night, while Australians get 8.1 hours. Late bedtimes seem to be to blame – people in Singapore tended to stay up until after 11.45 pm each night, while people in Australia were likely to hit the hay closer to 10.45 pm. The team found that, in general, national wake-up times were linked more to daylight hours than bedtimes. This could be because bedtimes are more affected by social factors. © Copyright Reed Business Information Ltd.
By Virginia Morell After defeating other males in boxing matches and winning a territorial roost—and a bevy of females—a male Seba’s short-tailed bat (Carollia perspicillata, pictured) might think his battles for reproductive rights are over. But the defeated males of this neotropical species have a trick up their sleeve: clandestine matings with willing females. The tactic works, and now researchers know why. Scientists studied bats in a captive colony in Switzerland, removing alpha males from their harems for 3 days, and examining their sperm—as well as that of their rivals. A previous study showed that the sneaky males have faster, longer lived sperm, which gives them a leg-up on the alpha male. Researchers had suspected this was because the sneakers produced this supersperm to compete. But the new study finds that after the 3 days of abstinence, the alpha male’s sperm is as agile and vigorous as that of his rivals. Thus, the team reports today in the Journal of Experimental Biology, the sneaky males aren’t generating special sperm—they just mate less, so their sperm is in better shape when it comes time to race to the egg. © 2016 American Association for the Advancement of Science.
By Sarah Kaplan The ancient Greeks spoke of a mythological society composed entirely of warrior women. The medieval traveler John Mandeville wrote of a place whose female rulers "never would suffer man to dwell amongst them." "Paradise Island," home of Wonder Woman, was a feminist utopia where no one with a Y chromosome was allowed. Sadly, those places only exist in fiction. But something like them does exist in the real world. It's in a wetland in rural Ohio. And it's full of salamanders. "They’re pretty incredible," said Robert Denton, a biologist at Ohio State who studies an unusual group of salamander species that literally don't need men. These creatures – all female – reproduce by cloning themselves. To keep their gene pool diverse, they sometimes "steal" sperm left behind on trees and leaves by male salamanders of other species and incorporate that DNA into their offspring. Most sexually reproducing organisms have two sets of chromosomes to make up their genome – one from each parent. But one of these strange salamanders can have between two and five times that much genetic material lying in wait within her cells. It's as if they have multiple genomes to fall back on, and that's made them incredibly successful. "Polyploid" salamanders have been around some 6 million years, Denton said — far longer than most other animal species that reproduce asexually. Since a lack of diversity means having a smaller arsenal of genetic variation to fall back on when living conditions change, these groups usually go extinct relatively quickly. © 1996-2016 The Washington Post
by Susan Milius There’s nothing like a guy doing all the child care to win female favor, even among giant water bugs. Thumbnail-sized Appasus water bugs have become an exemplar species for studying paternal care. After mating, females lay eggs on a male’s back and leave him to swim around for weeks tending his glued-on load. For an A. major water bug, lab tests show an egg burden can have the sweet side of attracting more females, researchers in Japan report May 4 in Royal Society Open Science. Given a choice of two males, females strongly favored, and laid more eggs on, the one already hauling around 10 eggs rather than the male that researchers had scraped eggless. Females still favored a well-egged male even when researchers offered two males that a female had already considered, but with their egg-carrying roles switched from the previous encounter. That formerly spurned suitor this time triumphed. A similar preference, though not as clear-cut, showed up in the slightly smaller and lighter A. japonicus giant water bug. “We conclude that sexual selection plays an important role in the maintenance of elaborate paternal care,” says study coauthor Shin-ya Ohba of Nagasaki University. © Society for Science & the Public 2000 - 2016
Nicola Davis Benedict Cumberbatch’s deep and booming voice might have made him a hit among women, but a low pitch is more likely to have evolved to intimidate other men, new research suggests. When both heterosexual men and women were played recordings of male voices, the deeper tones were hailed by men as sounding more dominant. While the deeper voices were judged to be more attractive by female listeners, the effect was weaker, the researchers report. “If you look at what men’s traits look like they are designed for, they look much better designed for intimidating other males than for attracting females,” said David Puts of Pennsylvania State University, who led the study. Published in Proceedings of the Royal Society B: Biological Sciences, the three-part study by an international team of scientists explored the links between voice pitch and mating systems, attractiveness and, for males only, perceived dominance. A formula for the perfect voice? Read more In the first leg of the research, the scientists turned their attention to primates encompassing Old and New World monkeys, as well as humans and other apes, to explore differences in “fundamental frequency” between males and females of each species - the aspect of the voice that is perceived as pitch. After selecting 1721 recordings, they found large differences were more common in polygynous species - where males mate with more than one female - than monogamous ones. That, they say, could be because in polygynous species, competition between males is greater - hence a male with a lower-pitched voice deemed to be intimidating could have the edge in securing a mate. Intriguingly, the researchers found that among the apes humans showed the greatest difference in pitch between the sexes, suggesting our ancestors were not searching for “the one” but were polygynous - a situation Puts still believes to be the case. © 2016 Guardian News and Media Limited
By Jordana Cepelewicz Everyone is familiar with the complaints of a hungry stomach. For years, scientists attributed the gnawing increase in appetite before a meal to ghrelin, a hormone which is secreted in the gut and circulates in the blood, playing a role in food intake and storage. Researchers have found that levels of ghrelin, dubbed the “hunger hormone,” peak before meals and recede after eating. Given its association with appetite, ghrelin is a tempting drug target for potential obesity treatments—but findings thus far have not lived up to expectations. Experiments that knock out the genes coding for ghrelin and its single receptor, GHSR (growth hormone secretagogue receptor), have been inconclusive: Remove the hormone or receptor, and rodents used in the experiments do not necessarily lose their drive to eat. Now a team of researchers at the French Institute of Health and Medical Research (INSERM) in Paris believe that scientists have had it wrong all along. In a study published this week in Science Signaling, they report that ghrelin does not enhance appetite in rats but rather increases weight gain and fat buildup. Unlike in earlier work, in the new study the researchers used a novel genetic method that kept the ghrelin receptor functional but modified it to have greater signaling in response to ghrelin—in other words, the receptor would enhance the hormone’s effects. The team then performed a series of experiments, first in isolated cells and then in rats. As expected, exposing ghrelin to modified receptors prompted a more potent response compared with the unaltered GHSR. © 2016 Scientific American
By Leonard Sax, M.D., Ph.D Why is it that girls tend to be more anxious than boys? It may start with how they feel about how they look. Some research has shown that in adolescence, girls tend to become more dissatisfied with their bodies, whereas boys tend to become more satisfied with their bodies. Another factor has to do with differences in how girls and boys use social media. A girl is much more likely than a boy to post a photo of herself wearing a swimsuit, while the boy is more likely to post a photo where the emphasis is on something he has done rather than on how he looks. If you don’t like Jake’s selfie showing off his big trophy, he may not care. But if you don’t like Sonya’s photo of herself wearing her bikini, she’s more likely to take it personally. Imagine another girl sitting in her bedroom, alone. She’s scrolling through other girls’ Instagram and Snapchat feeds. She sees Sonya showing off her new bikini; Sonya looks awesome. She sees Madison at a party, having a blast. She sees Vanessa with her adorable new puppy. And she thinks: I’m just sitting here in my bedroom, not doing anything. My life sucks. Boys are at lower risk for the toxic effects of social media than girls are, for at least three reasons. First, boys are less likely to be heavily invested in what you think of their selfies. “Does this swimsuit make me look fat?” is a question asked by girls more often than by boys. Second, boys tend to overestimate how interesting their own life is. Third, the average boy is likely to spend more time playing video games than Photoshopping his selfie for Instagram. And in video games, unlike social media, everybody truly can be a winner, eventually. If you play Grand Theft Auto or Call of Duty long enough, you will, sooner or later, complete all the missions, if you just keep at it. © 2016 The New York Times Company
By Patrick Monahan You might have seen a video from David Attenborough’s The Life of Birds series where a male superb lyrebird (Menura novaehollandiae) attempts to lure a mate by imitating a smorgasbord of bird calls and even chainsaws. As nature’s show-offs, male animals tend to have more elaborate colors and courtship behaviors than their female counterparts, so it’s typical that the male would get the public’s attention. The same is true in science: Plenty of female birds sing songs, but researchers have in the past often dismissed them as simply being evolutionary tag-alongs of the males’ “come hither” calls. Now, by recording the calls of female superb lyrebirds, researchers have found that they can keep up with the boys just fine. According to a study published this week in Frontiers in Ecology and Evolution, the females collectively imitated 19 other species of birds, and also sang lyrebird-specific songs. And they changed their songs depending on context, using more lyrebird-specific “whistle” calls when out foraging and vying for territory, but more mimicking calls when defending their nests (as in the audio file below). The fact that the females change their type of call depending on the context makes it likely that these songs evolved in their own right—and the males’ calls aren’t so special after all. Plus, that part about the chainsaw? It probably doesn’t even happen in the wild. © 2016 American Association for the Advancement of Science
Medical research and new drugs to treat human illness usually start with studies on mice and rats. But that type of research has been traditionally sexist — using far more male than female rodents. Scientists warn that has already led to drugs and treatments that are potentially dangerous for women and say the approach slows down the development of treatments and drugs that are safe and effective for everyone. Cara Tannenbaum, scientific director of the Institute of Gender and Health at the Canadian Institutes of Health Research, cited a couple of examples on CBC's The Current of cases where drug side-effects turned out to be far more harmful in women: A stomach drug called cisapride that was sold in the 1990s under the name Prepulsid was withdrawn by Health Canada in 2000 because it sometimes caused irregular heartbeat and sudden death "in women only," Tannenbaum said. Among the victims was the 15-year-old daughter of former Ontario MP Terence Young. "It's not clear that the drug was ever tested in female animals or minors," Tannenbaum added. Health Canada has issued a warning about sleeping pills containing the drug zolpiclone, also known as Ambien, Tannenbaum said. Women are recommended to take half the dose that is prescribed to men. "It was recently discovered that the level of the drug was 45 per cent higher in women the next day, which can lead to car accidents," Tannenbaum said. Jeffrey Mogil, a neuroscientist and pain specialist at McGill University, said there are lots of reasons to suspect men and women respond differently to many different kinds of drugs, but very little actual data. "We actually don't know the scope of the problem," he told The Current. ©2016 CBC/Radio-Canada.
Ian Sample Science editor The subtle impact of genetics on the age at which people lose their virginity has been teased apart by scientists and shown to have an effect on how well people fare at school. Though mostly driven by upbringing and peer behaviour, a person’s age when they first have sex is also shaped by biological factors where genes have a role to play. Researchers found that differences in DNA could account for a quarter of the variation in the age at which people lost their virginity, with other factors, among them religious beliefs, family background and peer pressure, making up the rest. Genes influence academic ability across all subjects, latest study shows Read more “We were able to calculate for the first time that there is a heritable component to age at first sex, and the heritability is about 25%, so one quarter nature, three quarters nurture,” said John Perry, an expert in reproductive ageing and related health conditions at Cambridge University. Among 38 sections of DNA found to affect the age at which people first had sex were genes that drive reproductive biology, such as the release of sex hormones and the age of puberty. Still others were found that appear to affect behaviour, personality and appearance. A variant of one of the genes, named CADM2, linked an early start to one’s sex life with risk-taking behaviour and having a large number of children. A version of another gene, MSRA, found in people who lost their virginity later than average, was linked to irritability. © 2016 Guardian News and Media Limited
By Lisa Sanders, M.D. On Thursday we challenged Well readers to take on the case of a 59-year-old woman who had not been able to stop gaining weight. I presented the case as it was presented to the doctor who made the diagnosis and asked for the final piece of data provided by the patient as well as the correct cause of her symptoms. I thought the tough part of this case was something that few of my readers would have to contend with – that her complaints and past medical history were quite ordinary. Like many of us, she was overweight and she came to the doctor because she had difficulty losing weight. In the background she also had high blood pressure, obstructive sleep apnea and low back pain, knee pain and leg swelling. These are some of the most common reasons patients seek medical attention. Although her problems were run of the mill, the cause was not. And many of you had no difficulty spotting this zebra. The correct diagnosis was… Acromegaly The last piece of data, provided by the patient, was a photograph taken several years before. It was only by seeing the changes in the patient’s face that had occurred over the past few years that the doctor recognized that this patient’s problem was unusual. The first person to make this diagnosis was Dr. Clare O’Connor, a physician in the second year of her training in internal medicine. She plans to subspecialize in endocrinology. She says it was the swollen legs that didn’t compress that gave her the first clue. Well done. Acromegaly is a rare disease caused by an excess of growth hormone, usually due to a tumor in the pituitary gland of the brain. The disease’s name, from the Greek, serves as a fitting description of the most obvious symptoms: great (mega) extremity (akron). The tumor secretes a protein called growth hormone that signals the liver to produce a substance called insulin-like growth factor 1, or IGF 1, which in turn tells cells throughout the body to start proliferating. © 2016 The New York Times Company
Scientists have outwitted the crafty rat with a stimulating new formula that puts sex on the brain. A team at Simon Fraser University in Burnaby, B.C., has developed a rat trap that combines synthetic sex pheromones, food scents and baby rat sounds to lure rodents to their deaths. The bait has proven 10 times more powerful than traditional traps and could be commercialized in about two years, said principal investigator Gerhard Gries. "Rats are really intelligent, and in order to manipulate them you have to be intelligent as well, and do that in a way that addresses their needs," said Gries, a communication ecologist in the department of biological sciences. "It smells delicious, it smells like rat and it sounds like rat." Research outlining the pheromone component of the control tactic was published last week in the international edition of the German peer-reviewed online journal Angewandte Chemie, which translates to "Applied Chemistry." The research on the use of baby rat sounds was published recently in the journal Pest Management Science. Gries worked for several years with research associates Stephen Takacs and Regine Gries, his wife, to develop the three-pronged extermination technique. Humans have waged war against the pests for more than 10,000 years, said Gerhard Gries, noting they spread disease, reduce agricultural crop yields and threaten endangered animal species. But rats are quick learners that have evolved to avoid traps, a behaviour called "neophobia," he said. ©2016 CBC/Radio-Canada.
By Nicholas Bakalar Hormone therapy for prostate cancer may increase the risk for depression, a new analysis has found. Hormone therapy, or androgen deprivation therapy, a widely used prostate cancer treatment, aims to reduce levels of testosterone and other male hormones, which helps limit the spread of prostate cancer cells. From 1992 to 2006, researchers studied 78,552 prostate cancer patients older than 65, of whom 33,382 had hormone therapy. Compared with those treated with other therapies, men who received androgen deprivation therapy were 23 percent more likely to receive a diagnosis of depression, and they had a 29 percent increased risk of having inpatient psychiatric treatment. Longer hormone treatment increased the risk: Researchers found a 12 percent increased relative risk with six or fewer months of treatment, a 26 percent increased risk with seven to 11 months, and a 37 percent increased risk with a year or more. The study, in The Journal of Clinical Oncology, is observational, and does not prove causation. The senior author, Dr. Paul L. Nguyen, of Brigham and Women’s Hospital, said that research is finding “almost an avalanche of side effects” with hormone therapy. Still, for some patients, especially those with severe disease, it can be a life saver. “You have to know what the potential upside is. For some guys it will still be worth it, but for some not.” © 2016 The New York Times Company
Carl Zimmer Five days a week, you can tune into “Paternity Court,” a television show featuring couples embroiled in disputes over fatherhood. It’s entertainment with a very old theme: Uncertainty over paternity goes back a long way in literature. Even Shakespeare and Chaucer cracked wise about cuckolds, who were often depicted wearing horns. But in a number of recent studies, researchers have found that our obsession with cuckolded fathers is seriously overblown. A number of recent genetic studies challenge the notion that mistaken paternity is commonplace. “It’s absolutely ridiculous,” said Maarten H.D. Larmuseau, a geneticist at the University of Leuven in Belgium who has led much of this new research. The term cuckold traditionally refers to the husband of an adulteress, but Dr. Larmuseau and other researchers focus on those cases that produce a child, which scientists politely call “extra-pair paternity.” Until the 20th century, it was difficult to prove that a particular man was the biological father of a particular child. In 1304 a British husband went to court to dispute the paternity of his wife’s child, born while he was abroad for three years. Despite the obvious logistical challenges, the court rejected the husband’s objection. “The privity between a man and his wife cannot be known,” the judge ruled. Modern biology lifted the veil from this mystery, albeit slowly. In the early 1900s, researchers discovered that people have distinct blood types inherited from their parents. In a 1943 lawsuit, Charlie Chaplin relied on blood-type testing to prove that he was not the father of the actress Joan Barry’s child. (The court refused to accept the evidence and forced Chaplin to pay child support anyway.) © 2016 The New York Times Company
Keyword: Sexual Behavior
Link ID: 22089 - Posted: 04.09.2016
Modern humans diverged from Neanderthals some 600,000 years ago – and a new study shows the Y chromosome might be what kept the two species separate. It seems we were genetically incompatible with our ancient relatives – and male fetuses conceived through sex with Neanderthal males would have miscarried. We knew that some cross-breeding between us and Neanderthals happened more recently – around 100,000 to 60,000 years ago. Neanderthal genes have been found in our genomes, on X chromosomes, and have been linked to traits such as skin colour, fertility and even depression and addiction. Now, an analysis of a Y chromosome from a 49,000-year-old male Neanderthal found in El Sidrón, Spain, suggests the chromosome has gone extinct seemingly without leaving any trace in modern humans. This could simply be because it drifted out of the human gene pool or, as the new study suggests, it could be because genetic differences meant that hybrid offspring who had this chromosome were infertile – a genetic dead end. Fernando Mendez of Stanford University, and his colleagues compared the Neanderthal Y chromosome with that of chimps, and ancient and modern humans. They found mutations in four genes that could have prevented the passage of Y chromosome down the paternal line to the hybrid children. “Some of these mutations could have played a role in the loss of Neanderthal Y chromosomes in human populations,” says Mendez. © Copyright Reed Business Information Ltd.
by Sarah Zielinski Spring has finally arrived, and birds’ nests all over the country will soon be filling up with eggs and then nestlings. Watch a nest long enough (the Science News staff is partial to the DC Eagle Cam) and you’ll see itty bitty baby birds begging for a meal. But mama birds don’t always reward that begging with food. In some species, like the tree swallow, birds that beg more will get more food. But in others, like the hoopoe, mom ignores who is begging and gives more food to the biggest chicks, researchers have found. This lack of an overall pattern has confounded ornithologists, but it seems that they may have been missing a key piece of the puzzle. A new study finds that the quality of the birds’ environment determines whether a mama bird can afford to feed all of her kids or if she has to ignore some to make sure the others survive. The study appears March 29 in Nature Communications. Stuart West of the University of Oxford and colleagues compiled data from 306 studies that looked at 143 bird species. When the birds were living in a good environment — one that had plenty of resources or a high amount of predictability — then mom would feed the chicks that beg the most, which were often the ones that needed the most help. But when the environment was poor in quality or unpredictable, then mama bird responded less to begging. |© Society for Science & the Public 2000 - 2016.
Keyword: Sexual Behavior
Link ID: 22079 - Posted: 04.07.2016
By Elizabeth Pennisi The “brrreeet” you hear in the video above is not coming from this broadbill’s beak, but rather from its wings. Charles Darwin marveled at “instrumental music” of birds—from the rattled quills of peacocks to the wing-drumming of grouse and the wing “booming” of night-jars. But those percussive noises are no match for the definitive tones generated by the three Smithornis broadbills (S. rufolateralis, S. capensis, and S. sharpei) that live in remote forests in sub-Saharan Africa. One bird acoustics specialist was so intrigued in 1986 by a recording of this “song,” that he vowed to hear it for himself. More than 2 years ago, he and his colleagues tracked two of these species down in the wild. Synchronized high-speed video and acoustic recordings revealed the downstroke of the wings produces the tones as the bird flies in a meter-wide oval from its perch and back again. At first the researchers thought the outermost flight feathers flutter to make the sounds, but studies of a wing and of the feathers themselves in a wind tunnel showed that the inner flight feathers are “singing” the most, the team reports today in the Journal of Experimental Biology. The tones may scale with the species’ body and feather size, with the bigger ones producing deeper tones, the researchers suggest. The wing tones seemed to have replaced vocal singing, they note, and are likely unique to this group of birds. Audible 100 meters away in dense forest, they represent yet another innovation for communicating with one’s peers. © 2016 American Association for the Advancement of Science
by Sarah Zielinski There must be something wrong with the guy who never leaves home, right? Maybe not — at least if that guy is a male spotted hyena. Males that stay with their birth clan, instead of taking off to join a new group, may simply be making a good choice, a new study suggests. Spotted hyenas are a matriarchal society. Females are in charge. They rank higher than every male in the clan. And the females generally stay with the clan for their entire lives. But males face a choice when they reach two and a half years in age. They can stay with the clan, or they can leave and join a new clan. Each choice has its pros and cons. Staying with the clan means that a male hyena keeps a place at the top of the male pecking order. He’ll probably have his mother around to help. But he’ll be limited in the number of females he can mate with, because many of the female hyenas won’t mate with him because they might be related. If he joins a new clan, the male hyena might have access to more females — and they might even be better than the ones in his home clan — but he’ll start with the lowest social rank and have to spend years fighting his way to the top. Among most group-living mammal species, the guys that stay at home turn out to be losers, siring fewer offspring. But spotted hyenas, it appears, are an exception. Eve Davidian of the Leibniz Institute for Zoo and Wildlife Research in Berlin and colleagues tracked 254 male spotted hyenas that lived in eight clans in Ngorongoro Crater in Tanzania throughout their lives, a study lasting 20 years. When these males reached the age of maturity, they left their clans to take a look at the other options available to them. Forty-one hyenas returned to their home clans, and 213 settled with new ones. © Society for Science & the Public 2000 - 2016
By Daisy Yuhas Something was wrong with Brayson Thibodeaux. At 15 months old, he still was not walking; his parents and grandparents were certain that his development was slower than normal. After pushing doctors for answers they finally got him to a neurologist who recommended a genetic test. Brayson had fragile X syndrome, the leading heritable cause of intellectual disability and of autism. The discovery sent ripples through the extended family, who live outside New Orleans. Brayson’s great-grandmother, Cheryl, recalled having heard of fragile X and discovered a cousin whose grandson had the same condition. She soon learned that many members of her family were confirmed carriers of a genetic condition—the fragile X pre-mutation—that put them at risk of having children with this syndrome. “Fragile X” refers to a mutation that alters the X chromosome in such a way that, viewed under a microscope, it would look like a piece was about to break off. That is because one gene contains multiple repetitions of noncoding DNA—specifically CGG (cytosine, guanine, guanine). The exact number of CGG repetitions is variable, but when it reaches more than 200, it is considered to be the full mutation, which causes the syndrome. People with between 55 and 200 repeats are said to have a partial or pre-mutation, an unstable gene that can expand into the full mutation in future generations. © 2016 Scientific American,