Why does the giraffe have such a long neck? Analysis zeroes in on genes

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1 Why does the giraffe have such a long neck? Analysis zeroes in on genes By Washington Post, adapted by Newsela staff on Word Count 741 A 4-day-old baby giraffe stands near her mother Denisa at Ramat Gan Safari, near Tel Aviv, Israel, in Photo: Reuters/Gil Cohen Magen Giraffes: They're weird. Their long necks and short bodies are examples of how animals adapt during evolution. Evolution is the theory that species change over time to become better at living in their environment. The changes that make the animals' bodies better suited to their environment are called adaptations. Giraffes' bodies are short to support their long necks. Their legs grow super straight to keep them from bending under pressure. Their blood pressure is twice as high as ours, letting them pump blood more than 6 feet up to reach their brains. Scientists know that these adaptations all happened fairly quickly as far as evolution goes. Eleven million years ago, the giraffe and the okapi first became their own species. The okapi is the giraffe's closest living relative, and they share a common ancestor. Since then, the giraffe has changed its appearance to what we recognize today. The okapi has kept the zebra-like appearance of their ancestors.

2 Comparing The Giraffe With Its Relative, The Okapi But the differences were probably the result of a few small changes in the giraffe's genes. Genes are sections of DNA that tell a specific part of the body how to grow and work. A genome is made of up DNA and genes. It contains all of the information about a living thing's body and how it works. The first full giraffe and okapi genome sequences were published on Tuesday in Nature Communications. Two scientists, Douglas Cavener and Morris Agaba, conducted the study. Cavener and Agaba compared genomes of giraffes, okapi, and 40 other animals including humans. The scientists wanted to figure out what genes might give giraffes their qualities. The okapi and giraffe genomes are very similar. Therefore, any differences could be used to find the genes behind long necks and powerful hearts. Instead of completely new genes, they found 70 genes with changes only giraffes have. There's a belief that to make something new in evolution, there has to be a big DNA change, but that is not true, Cavener said. Small DNA changes can have major effects. That Long Neck Needs To Be Paired With Sturdy Heart Most of the genes Cavener and Agaba found help determine how the bodies of other animals form. This supports the idea that tweaking these genes could change an animal's physical qualities. For example, a small change in genes could make a donkey-like creature incredibly tall. The scientists found some genes that affect the forming of both the skeletal and cardiovascular systems of animals. The idea that a gene would affect the skeletal system, or bones, and cardiovascular system, or heart and system for transporting blood, at the same time makes sense. A giraffe needs a strong heart to go along with its long neck. Changes in genes that affect both systems could have created long necks and strong hearts to support them. Giraffes might not have survived a change in the skeletal system alone. More research is needed to know whether these genes are really the cause of giraffes' long necks. Cavener said that many little changes went into giraffe evolution. Researchers are just scratching the surface of all the changes in genes, he said. Cavener plans to test out some of these genes soon. He and his team will breed mice with altered DNA. Cavener's team will replace some of the mouse genes with giraffe genes. With luck, they will see some familiar-looking skeletal or cardiovascular changes in the mice. Using Data To Help Human Hearts The scientists hope to learn how these creatures handle such high blood pressure without injury. Understanding how giraffes do this could help develop treatments for humans. The study of the giraffe genomes will also have more immediate uses. The team plans to look

3 at the genomes of possible subspecies of giraffe. A subspecies is another group within a species with shared qualities. The scientists will try to learn whether the possible giraffe subspecies are actually different from one another. If the subspecies are distinct from one another, then some of them are endangered, Cavener said. Giraffe populations have fallen by two-fifths over the past 15 years. This is because giraffes are illegally hunted and land they live on is being taken from them. There could be fewer than 10,000 giraffes left by the end of the century. Some specific types of giraffe, or subspecies, could disappear even sooner. The genome sequences could help to find those subspecies, Cavener said.

4 Quiz 1 Which sentence from the section "Comparing The Giraffe With Its Relative, The Okapi" BEST helps the reader understand the meaning of "genome"? But the differences were probably the result of a few small changes in the giraffe's genes. It contains all of the information about a living thing's body and how it works. The scientists wanted to figure out what genes might give giraffes their qualities. Instead of completely new genes, they found 70 genes with changes only giraffes have. 2 According to the article, what allowed giraffes to develop and survive with such long necks? genes that changed their skeletal and cardiovascular systems at the same time genes that allowed their skeletons to grow twice as fast as other species, like the okapi extremely low blood pressure that keeps them from getting dizzy and falling over extremely long legs that make them able to balance their heavy bodies and long necks 3 Read the sentence below. This supports the idea that tweaking these genes could change an animal's physical qualities. What other word from the sentence helps the reader understand the meaning of the word "tweaking"? supports idea change physical

5 4 Read the section "Using Data To Help Human Hearts." According to the article, how could the giraffe research be helpful in the future? It could help more people understand what a subspecies is. It could help scientists define what genomes are. It could help scientists treat human diseases. It could help convince people to stop hunting giraffes.

6 Answer Key 1 Which sentence from the section "Comparing The Giraffe With Its Relative, The Okapi" BEST helps the reader understand the meaning of "genome"? But the differences were probably the result of a few small changes in the giraffe's genes. It contains all of the information about a living thing's body and how it works. The scientists wanted to figure out what genes might give giraffes their qualities. Instead of completely new genes, they found 70 genes with changes only giraffes have. 2 According to the article, what allowed giraffes to develop and survive with such long necks? genes that changed their skeletal and cardiovascular systems at the same time genes that allowed their skeletons to grow twice as fast as other species, like the okapi extremely low blood pressure that keeps them from getting dizzy and falling over extremely long legs that make them able to balance their heavy bodies and long necks 3 Read the sentence below. This supports the idea that tweaking these genes could change an animal's physical qualities. What other word from the sentence helps the reader understand the meaning of the word "tweaking"? supports idea change physical

7 4 Read the section "Using Data To Help Human Hearts." According to the article, how could the giraffe research be helpful in the future? It could help more people understand what a subspecies is. It could help scientists define what genomes are. It could help scientists treat human diseases. It could help convince people to stop hunting giraffes.