Name___________________________________________Per_____

Science: What Is DNA? Every cell in every living thing (or organism) has DNA, a molecule that contains all the information about that organism. Building on research by others before them, the structure of DNA was discovered in 1953 by the British scientist Francis Crick and the American scientist James Watson. James Watson was a World Almanac reader as a kid.

Lengths of connected DNA molecules, called genes, are like tiny pieces of a secret code. They determine what each organism is like in great detail. Almost all the DNA and genes come packaged in rod-like structures called chromosomes—humans have 46. There are 22 almost identical pairs, plus the X and Y chromosomes, which determine if a human is male (one X chromosome and one Y chromosome) or female (two X chromosomes).

Genes are passed on from parents to children, and no two organisms (except clones and identical twins) have the same DNA. Many things—the color of our eyes or hair, whether we're tall or short, our chances of getting certain diseases—depend on the genes we get from

our parents.

DNA "Fingerprints" DNA is located in each of your cells, including your blood, saliva, hair follicles, and skin. No one else has a DNA pattern exactly like yours. For these reasons, DNA evidence can be collected from skin or hair collected a crime scene and then be

linked to a suspect. Scientists can analyze the exact makeup of the two sets of DNA, and if they are identical, chances are that they are from the same person. Cells from a person at a crime scene can be evidence enough to convince a jury that that person was present at the crime.

DNA evidence is also helping show that some wrongly accused and convicted people are innocent. Since 1992, DNA evidence has helped reverse at least 78 convictions (including 10 cases where the death penalty was involved). In January 2001, a man imprisoned for murder in Texas was released because of DNA tests. Another man, sentenced to death for a murder in Virginia in 1982, was set free in February. New evidence based on DNA tests cleared him of the crime.

The Human Genome The human genome is the DNA code for our species—it's what makes us human beings. In 2000, the U.S. Human Genome Project reached a milestone in a 15-year study of the human genome. It identified the 3.1 billion separate codes in human DNA. In early 2003, researchers succeeded in mapping out all the human chromosomes.

The human genome contains 20,000 to 25,000 genes. That's around the same number of genes as a roundworm — and it's fewer than the 50,000-plus genes of a rice plant! But unlike the genes of most living things, human genes are able to produce more than one kind of protein, a phenomenon called "alternative splicing." Proteins perform most life functions and make up a large part of cellular structures.

By studying human genes, scientists can learn more about hereditary diseases and get a better idea of how humans evolved.

Questions for “Science: What is DNA?”

1. The article defines “genes” as:

2. Humans have ______total chromosomes.

3. The chromosomes that determine sex are the _____and the_____chromosome.

4. In your own words, describe how DNA can be used to solve crime.

5. The article defines “human genome” as

6. There are ______________________________genes.

7. T or F: We have more genes than the rice plant.

Citation: "Science: What Is DNA?." The World Almanac for Kids. 2006. Facts For Learning. Facts On File News Services. June, 2006 <http://factsforlearning.2facts.com>.

Discovery Education 2006. All Rights Reserved. page 2