Who Discovered DNA?

Who Discovered DNA? — page 3 — Heredity in practice 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 8

Who Discovered DNA? — page 4 — Old beliefs survive For centuries people knew from experience that living things produce others like themselves that a human mother could not for example give birth to a rabbit Yet not everyone was quite sure whether this was impossible and they did believe that a mother’s experiences affected the way her young looked For example many people thought that if a baby was born with a cleft palate a condition that affects the top lip sometimes called a harelip the mother must have come into contact with a hare while pregnant Similar superstitions still survive all over the world THAT’S A FACT In 1726 an English woman named Mary Toft claimed to have given birth to rabbits Somehow she managed to convince two doctors that it was the result of dreaming about rabbits and craving rabbit meat Most doctors were sure this was wrong Eventually she admitted it was all a hoax done for money About 12,000 years ago people began to train wild wolves like this one to help with hunting Since then they have used selective breeding to produce the different kinds of dogs we see today Breakthrough People learned from experience that living things produce young like themselves They learned to choose the best plants and animals to breed Over the years they developed productive crops from wild plants and farm animals from wild creatures 9

Who Discovered DNA? — page 5 — How are living things made It was all perforated and porous much like a honeycomb these pores or cells were indeed the ﬁrst microscopical pores I ever saw and perhaps that were ever seen Robert Hooke from Micrographia talking about his observations of cork bark Pictured below are the magniﬁed cells of cork bark drawn by the scientist Robert Hooke and ﬁrst published in 1665 Hooke was the ﬁrst person to coin the term cells for these tiny parts of living things Building blocks By the 17th century both farmers and scientists knew they could inﬂuence heredity but no one knew how it worked To know how organisms worked scientists needed to ﬁnd out what organisms are made from and how they are put together This important step was made just under 350 years ago by an English scientist named Robert Hooke Hooke was born in 1635 and as a young man studied many different scientiﬁc subjects He was a genius at making and using scientiﬁc instruments One of these instruments was a microscope Cells Hooke examined many different things through his microscope In 1665 he published Micrographia a book about the things he had seen It contained one of his most famous drawings an enlarged section of a piece of cork bark The bark was made up of tiny sections that he called cells after the tiny cells that monks slept in 10

Who Discovered DNA? — page 6 — What are cells We now know that cells are filled with a salty substance called cytoplasm but they also contain tiny working parts called organelles The most important of these organelles is the nucleus which controls what the cell does Most but not all of the DNA in a cell is in the nucleus In order for an organism to grow and repair any damage to itself new cells must grow New cells come from the division of old ones Cells divide making two new cells almost identical to each other This is called mitosis Cell membrane Cytoplasm Original cell Organelle Nucleus Cells reproduce by dividing over and over again Before a cell divides everything inside it including its central nucleus is duplicated The cell then gradually splits into two identical new cells Animal cells The wall of a plant cell is fairly thick so it is easy to see under a microscope Animal cells lack cell walls and are instead surrounded by a membrane which is not as obvious as a wall In the 1830s German scientist Theodor Schwann was one of the ﬁrst to see animal cells In 1839 he and fellow scientist Matthias Jacob Schleiden published their theory that all living things are made of cells They went on to ﬁnd out more about what happens inside a cell The original cell has divided into two new cells Breakthrough Robert Hooke made better microscopes than most of those made previously Through them he saw parts of organisms too tiny to see before He and others after him discovered that cells make up all living things They are among the basic building blocks of life 11

5

PAGE 5 OF 41

The only kids' eBook subscription service that offers thousands of high-quality books from well known publishers like HarperCollins, National Geographic and others.

JavaScript Required

Whoops! We're sorry but Epic doesn't work properly without JavaScript enabled. Check your web browser's settings to make sure it's enabled.