Jenny Vaughan - Who Discovered DNA?

E-book published in 2015 by Encyclopdia Britannica, Inc., in association with Arcturus Publishing Limited, 26/27 Bickels Yard, 151-153 Bermondsey Street, London SE1 3HA. Britannica, Encyclopdia Britannica, and the Thistle logo are registered trademarks of Encyclopdia Britannica, Inc.

ISBN 978-1-62513-312-0 (e-book)

This edition first published in 2010 by Arcturus Publishing

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Library of Congress Cataloging-in-Publication Data

Vaughan, Jenny, 1947

Who discovered DNA? / Jenny Vaughan.

p. cm. -- (Breakthroughs in science and technology)

Summary: Looking at some of the major inventions and discoveries shaping our world today, Breakthroughs in Science profiles the research leading up to the discovery (not just profiles of the one or two key players). Each book describes the famous moment and then examines the continued evolution illustrating its impact today and for the future-- Provided by publisher.

Includes index.

1. DNA--Juvenile literature. I. Title.

QP624.V38 2011

572.86--dc22

2010011021

Picture Credits

Corbis: cover (Dennis Scott), 8 (The Gallery Collection), 14 (Jeff Vanuga/Jeff Vanuga, Dubois, Wyoming), 36 (Jo Yong-Hak/Reuters), 40 (Amy Toensing/Sygma), 43 (Yonhap/epa). Getty Images: 31 (Science VU/Drs. H. PotterD. Dressler), 34 (Sam Yeh/AFP). iStockphoto.com: 41 (Hans Laubel). Library of Congress: 29. Science Photo Library: 10 (Omikron), 17 top (JJP/Philippe Plailly/Eurelios), 18 (Dr. Jeremy Burgess), 21 (Kwangshin Kim), 23, 24 (A Barrington Brown), 28 (Ria Novosti), 39 (Corbin OGrady Studio). Shutterstock Images: title page and 25 (Matthew Cole), 6 (Eric Gevaert), 7 (Alexander Raths), 9 (Geoffrey Kuchera), 12 (R Nagy), 19 (Michael Ledray), 22 (Damian Palus), 33 (Christophe Buquet), 32 (Pedro Salaverra), 35 (Henrik Larsson), 38 (Colette3). Wikimedia Commons: 13 (Linda Hall Library), 16.

Every attempt has been made to clear copyright. Should there be any inadvertent omission, please apply to the copyright holder for rectification.

The author would like to thank John Farndon for his invaluable help and advice in writing this book.

SL001445US Supplier 03, Date 0510

Contents

An age-old mystery

What makes us the way we are? Why do some of us have dark hair and others have light hair? Why do cats only have kittens and never puppies?

For centuries, no one knew the answers to these questions. It took many years of inquiry and research to understand how organisms (living things) inherit characteristics from their parents.

Two kinds of study

Two different kinds of study led to this understanding. One involved breeding plants and animals and noticing how living things pass their characteristics, such as color, size, and shape, to their offspring. This is called heredity.

Another area of study looked at how organisms are constructed. Scientists learned that organisms are all made up of tiny building blocks called cells. The very smallest living things, such as bacteria, are made up of just one cell, while large organisms, such as humans, have trillions of cells.

T HATS A F ACT !

Some bacteria are so small that a million can cover the head of a pin.

Sheep, like other living things, produce offspring like themselves. The young inherit characteristics from their parents. In this case, young lambs, like adult sheep, will have four legs, will eat grass, and will have thick, woolly coats.

This photograph shows bacteria being grown in a laboratory. Bacteria are single-celled organisms that reproduce by dividing in two. They reproduce very quickly to make new organisms that are like the original ones.

Eventually, scientists discovered that living things pass on their characteristics through something that is found in living cells. That something is an extraordinary substance called deoxyribonucleic acid, or DNA.

A great breakthrough

Discovering DNA and how it works was one of the greatest breakthroughs in science in the last 100 years. Today, scientists know not only how DNA works but also how to use DNA to give living things characteristics they could never have naturally. They can make clonesexact copies of organisms. They are beginning to create life synthetically (from scratch) in a laboratory.

Life needs life

Until as late as the 1800s, many scientists believed that some living things appeared spontaneouslythat is, without any parents. For example, food that was left out would spoil when tiny germs (we now call them bacteria) appeared in it.

French biologist Louis Pasteur set out to show that even the tiniest life-forms had to come from somewhere. In a set of experiments, he boiled beef broth to kill any existing germs. Then he kept the broth in flasks with special filters to keep out any dust or particles. No germs grew in the broth. But when he opened the flasks to the air, the broth soon spoiled.

Pasteur showed that bacteria did not appear spontaneously, which confirmed earlier work by 17th-century scientist Francesco Redi.

I prefer to think that life comes from life, rather than from dust.

Louis Pasteur

Breakthrough

Louis Pasteur proved that life does not appear spontaneously. His experiments with bacteria showed that living things are produced only by other living things like themselves.

The first farmers

Even in ancient times, people discovered they could influence heredity. When early humans started to settle in one place, they began to grow the food they needed instead of hunting and foraging for it. These were the first farmers. Over many years, they turned wild grasses into cereal crops such as wheat, barley, rice, maize, millet, and sorghum. They did this in a process called selective breeding. They collected the seeds from the best plants of one generation of crops to produce the next generation of plants. Better, tastier vegetables were also produced this way.

Farmers realized that animals could be changed by selective breeding, too. They bred animals that had characteristics or traits they wanted, such as cattle with more meat and dogs that were easy to train for hunting or herding. But even though farmers had discovered that they could influence heredity, they did not understand what made this possible.

These pictures are from ancient Egypt, and date from around 4,000 years ago. They show us that people had by then already developed grain crops from grasses and bred farm animals from wild ones.