Mutations: Not Just for Superheroes PDF

Mutations: Not Just for...

Mutations: Not Just for Superheroes Mutations: Not Just for Superheroes © 2018 The Regents of the University of California. All rights reserved. Permission granted to purchaser to photocopy for classroom use. Image Credit: iStockphoto. Chapter 1: Movie Mutations In movies, mutations are always exciting: they might give someone special powers or extra limbs. However, real mutations can be very boring: they might not have any noticeable effect at all. What is a mutation, anyway? The answer has to do with genes and the way they are passed down when organisms reproduce. Genes are instructions for making protein molecules, and those protein molecules determine an organism’s traits. When In movies and comic books, mutations make organisms reproduce, they pass down copies people into superheroes. In the real world, of their genes to their offspring. However, mutations often have no visible effect at all. the copies aren’t always perfect: as genes are duplicated, changes can occur. These changes are called mutations, and they can be passed from parent to offspring when organisms reproduce. Most of the changes are minor and don’t affect traits at all, but every once in a while, mutated genes give instructions to make a new protein molecule that leads to a new trait in the offspring. The new traits that arise from mutations may be adaptive or non-adaptive, or they may have no effect on survival and reproduction. It all depends on the organisms’ environment. If a new trait makes organisms less likely to survive and reproduce in their environment, the trait is non-adaptive. Organisms born with that trait don’t have a very good chance of surviving long enough to reproduce and pass their mutated genes down to the next generation. If they don’t pass the mutated genes down, they don’t pass the new trait down either. Mutated traits that are non-adaptive usually remain uncommon in the population. Mutations: Not Just for Superheroes 1 On the other hand, mutated genes sometimes result in a new trait that turns out to be adaptive. Adaptive traits help organisms survive and reproduce in their environments. If a mutation results in an adaptive trait, organisms with that trait are more likely to reproduce and pass on their mutated genes to the next generation. Through natural selection, adaptive traits become more and more common in the population over time. A trait that is adaptive Mutations: Not Just for Superheroes © 2018 The Regents of the University of California. All rights reserved. Permission granted to purchaser to photocopy for classroom use. in one environment may be non-adaptive in another, and that’s what makes mutations so important. Environments don’t stay the same forever. Mutations can introduce new traits, increasing the chance that one of those traits might help make a population better able to adapt to a changing environment. To learn more about mutations, you can explore one or more of the following chapters. 2 Mutations: Not Just for Superheroes  Chapter 2: Revenge Mutations: Not Just for Superheroes © 2018 The Regents of the University of California. All rights reserved. Permission granted to purchaser to photocopy for classroom use. Image Credit: Science Source; Janice Haney Carr/CDC. of the Bed Bugs They creep into your bed at night and suck your blood, then crawl back to hide in their lairs… Bed bugs are seriously creepy! These tiny insects live in walls and furniture, and they survive by feeding on the blood of humans. Bed bugs have been a problem for humans for thousands of years. In the past, people didn’t have any good way of attacking bed bugs—these insects hide during the day, only coming out at night when people are sleeping. People couldn’t kill bed bugs by leaving poison for them to eat, because they won’t eat anything but blood. Then, in the 1940s, the situation changed: people invented new insecticides that were very effective at killing bed bugs. Like all insects, bed bugs have hard exoskeletons covering their bodies like suits of armor. However, the Bed bugs live inside walls and furniture and new insecticides penetrated the bed bugs’ survive by feeding on the blood of humans. exoskeletons, killing bed bugs even if they just touched the insecticide. People sprayed these new insecticides wherever bed bugs were found, and killed huge numbers of bed bugs. The insecticides didn’t kill all of the bed bugs, however. In fact, they caused some effects that people hadn’t predicted. Some bed bugs survived—mostly the individuals lucky enough to have extra-tough exoskeletons that were harder for insecticides to penetrate. These tough-skinned bed bugs began reproducing. Today, bed bugs with extra- tough exoskeletons are becoming more and more common in the bed bug population. Scientists have studied the genes of tough- skinned bed bugs and compared them to the genes of ordinary bed bugs. They discovered mutations to several genes in the tough-skinned bed bugs. The mutations give the cells instructions to make protein molecules different from the protein molecules that other bed bugs can make. These new Mutations: Not Just for Superheroes 3 protein molecules all affect the exoskeleton bugs with that trait survive. In the bed bugs’ in different ways, strengthening the bed new insecticide-filled environment, stronger bugs’ armor. Before these mutations armor is an adaptive trait that helps them appeared in the bed bug population, there survive. Organisms with stronger armor are weren’t any bed bugs with the trait of armor more likely to survive and reproduce, so they strong enough to resist insecticides. are more likely to pass on their mutated genes— and their adaptive traits. Through the process The bed bugs’ environment changed when of natural selection, tough-skinned bed bugs people started using the new insecticides. are becoming more common with each new However, a mutated trait in the bed bug generation. Ironically, people’s use of insecticide population turned out to be adaptive in the bed has produced a stronger bed bug population! bugs’ new environment, so it helped the bed Mutations: Not Just for Superheroes © 2018 The Regents of the University of California. All rights reserved. Permission granted to purchaser to photocopy for classroom use. All bed bugs have exoskeletons, but some exoskeletons are thicker than others due to mutations. 4 Mutations: Not Just for Superheroes  Chapter 3: Cane Toad Invaders to keep moving into new areas with more food sources. The first toads to reach new Huge poisonous toads have invaded Australia! territory get to eat all the food they want. Humans brought cane toads from Asia to Slower toads are stuck with whatever is left. Australia in the 1930s, hoping the toads would eat beetles that were destroying crops. Recently, Australian scientists have been Mutations: Not Just for Superheroes © 2018 The Regents of the University of California. All rights reserved. Permission granted to purchaser to photocopy for classroom use. Image Credit: Shutterstock. Unfortunately, the toads didn’t eat many finding cane toads with bigger, more muscular beetles. They ate almost anything else that legs. These bigger legs can be traced back could fit into their mouths, however. These to mutations that changed the toads’ genes. big toads grow up to 22 centimeters (9 Scientists compared the big-legged toads to inches) long and weigh up to 1.8 kilograms (4 ordinary cane toads. They identified several pounds). Cane toads are extremely poisonous, gene mutations that gave the cells instructions and no Australian predators can survive to make protein molecules that were different eating them. Without predators in their from the protein molecules that other toads new environment, the cane toad population could make. These new protein molecules began growing and spreading. Today, cane affected the cane toads’ legs, increasing the toads are common in areas more than 1,500 leg size and strength. Having bigger legs is an kilometers (932 miles) from the place where adaptive trait that helps cane toads survive they were first introduced to Australia. in an environment where there isn’t much food to go around. Bigger, stronger legs help Because there are so many cane toads in these toads outrun other cane toads and Australia, they compete with each other for be the first ones to get to the food in new food. The cane toads are eating everything areas. With better chances of getting food, in sight, so food becomes scarce in any area big-legged toads are more likely to survive where they live. To survive, cane toads have and reproduce. Because of this, they are also Cane toads like this one can grow up to 22 cm (9 in) long and weigh up to 1.8 kg (4 lbs). Mutations: Not Just for Superheroes 5 more likely to pass on their mutated genes to their offspring. Along with these mutated genes, they pass on their adaptive traits. When humans introduced cane toads to Australia, the cane toads’ environment changed. With no predators hunting them in their new environment, there were more cane toads and therefore much less food was available. However, mutations led to a new trait in the population that turned out to be adaptive in the new environment. The mutated trait for Mutations: Not Just for Superheroes © 2018 The Regents of the University of California. All rights reserved. Permission granted to purchaser to photocopy for classroom use. bigger legs was adaptive for cane toads in an environment with scarce food because it helped them get more food and survive. Through the process of natural selection, big-legged cane toads are becoming more and more common in the cane toad population. These stronger, faster toads are spreading across Australia, invading new areas all the time. Through the process of natural selection, cane toads with big, strong legs are becoming more and more common in the cane toad population. 6 Mutations: Not Just for Superheroes Mutations: Not Just for Superheroes © 2018 The Regents of the University of California. All rights reserved. Permission granted to purchaser to photocopy for classroom use. Image Credit: Betty Holmes/NEFSC/NOAA; Shutterstock. Chapter 4: Red Lobster, Blue Lobster What color are lobsters? In pictures, they’re usually red. However, that’s only after they’ve been caught and cooked. When they’re alive and living in the ocean, lobsters are usually a greenish brown that blends into the ocean floor—except when a genetic mutation causes them to be bright blue! About one in every two million wild lobsters is blue in color. Why? A genetic mutation caused the lobster’s body to produce more of a certain protein molecule than usual, which turned its shell blue instead of the normal brownish green. This mutation introduced a new trait into the lobster population: bright blue shells. Having a blue shell may sound like the kind of trait that might make a lobster less likely to survive in its environment. After all, blue Most lobsters are greenish-brown. lobsters don’t blend into their environment as well as greenish-brown ones do. However, research shows that being blue doesn’t seem to make the blue lobsters any more or less likely to survive in their environments. In the 1990s, scientists studied blue lobsters: they mated a female blue lobster with a male blue lobster, producing all blue offspring. They released the offspring into the wild and studied them to see whether they survived at the same rates as lobsters with normal greenish-brown coloring. The scientists found no difference in the blue lobsters’ survival rates compared with normal lobsters. The genetic mutation that results in blue shells appears to be a neutral mutation—that is, the trait is not adaptive in the environment, but it’s not non-adaptive either. Blue shells seem to have no effect on survival and reproduction. The trait for blue shells has not caused a big change in the lobster population. The mutated trait still passes from one lobster generation to the next, just like the traits for About one in every two million lobsters has a greenish-brown shells. Lobsters with blue mutation that causes its shell to be bright blue. Mutations: Not Just for Superheroes 7 shells are just as likely to survive as lobsters with greenish-brown shells, so lobsters with these two color traits are likely to have about the same number of offspring. That means that the mutated trait has become neither more common nor less common in the population. Lobsters also come in other colors: occasionally, people catch lobsters that are yellow, orange, red, or white! All of those other colors are also caused by genetic mutations. These rare lobsters’ colors make them stand Mutations: Not Just for Superheroes © 2018 The Regents of the University of California. All rights reserved. Permission granted to purchaser to photocopy for classroom use. out in a crowd of living lobsters, but once cooked, colorful lobsters look just like their brownish-green relatives: like nearly all other lobsters, they turn bright red when boiled. (The only lobsters that don’t turn color when they’re cooked are extremely rare albino lobsters, which have no coloring at all.) 8 Mutations: Not Just for Superheroes