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The doorbell rings. Busy in the kitchen fixing dinner, Nancy's dad yells out, "Answer the door, Nancy! My hands are full!" Nancy opens the front door and suddenly, a bunch of people she hasn't seen in 3 years pour into the house.

Aunt Rita hands Nancy a wrapped package and says, "Well, look at you! How you've grown. And you've got such beautiful, red, curly hair! It runs in the family, you know. You look just like my grandmother!" Uncle Michael adds, "And she's going to be tall, like her father. Only 9 years old, and she looks like a basketball player already!"

Nancy makes a dash to the kitchen wondering, "Huh? Aunt Rita's grandmother? Runs in the family? Basketball? What are they talking about?"

Genes (say: jeenz), that's what they're talking about. Genes are the things that determine physical and other traits: tall or short, curly or straight hair, long legs or arms, or blue or green eyes. Keep reading to learn more about genes and how they work.

What Is a Gene?
The human body contains about 30,000 genes, which are pieces of information that determine your traits (say: trates). Traits are characteristics you inherit from your parents. Your parents pass along information in the genes that make you who you are. For example, if both of your parents have green eyes, you might inherit the trait of green eyes from them. Or if your mom has freckles, you might inherit that trait. In both cases, the information in the genes that they give you determines who you are, whether you have green peepers, or you're a freckle face. And genes aren't just in humans: all animals and plants have genes, too.

Genes hang out all lined up on thread-like things called chromosomes (say: kro-moh-somes).There are hundreds, sometimes thousands of genes, in one chromosome. Chromosomes come in pairs.

Chromosomes are located inside cells. A cell is so tiny you can only see it through the lens of a microscope, and there are billions of cells in your body. Most cells have one nucleus (say: noo-clee-us). The nucleus, which is sort of egg-shaped, is like the brain of the cell. It tells every part of the cell what to do. How does the nucleus know so much? As tiny as it is, the nucleus has more information in it than the biggest dictionary you've ever seen. Instead of looking up information in a book, though, the nucleus can find anything it needs to know about you in your genes.

In humans, a cell nucleus contains 46 individual chromosomes or 23 pairs of chromosome (chromosomes come in pairs, remember? 23 X 2 = 46). Half of these chromosomes come from one parent and half come from the other parent. But not every living thing has 46 chromosomes in its nucleus. A fruit fly cell has only 4 chromosomes in its nucleus.

How Do Genes Work?
Each gene has a special job to do. It carries a blueprint - the special instructions - for making a special protein in the cell.
Bones and teeth, hair and fur, earlobes and tails, muscles and toes, blood and other important chemicals in the body, all are made up of proteins (as well as other stuff). Humans have about 30,000 different kinds of proteins!

Like chromosomes, genes also come in pairs. Each of your parents has two sets of genes and each of your parents passes along just one gene from their pair to make up the set you have. Single genes or groups of genes that are passed on to you determine your traits, such as your hair color, height, and skin color.

Maybe Nancy's mother has one gene for brown hair and one for red hair, and she passed the red hair gene on to Nancy. If her father has two genes for red hair, that could explain her red hair. Nancy ended up with two genes for red hair, one from each of her parents.

You easily can see genes at work if you think about the many breeds of dogs there are. They're all dogs, but they look so different. Some breeds have short or long, straight or curly fur. Some dogs have brown, black, white, or red fur. Some breeds weigh only 3 or 4 pounds and other breeds weigh over 100. Dalmatians have genes for white coats and black spots. Toy poodles have genes that make them small with a curly coat and a little bark.

When There Are Problems With Genes
Scientists are very busy studying genes. What does each one do in the body? What illnesses are caused by genes that don't work right? Researchers think faulty genes may be partly to blame for
lung problems, cancer, and many other illnesses.

Take the gene that helps the body make hemoglobin, for example. Hemoglobin is an important protein that is needed in your red blood cells to carry oxygen throughout your body. If parents pass on faulty hemoglobin genes to their child, the child may only be able to make a type of hemoglobin that doesn't work properly. This can cause a condition known as anemia, which can make that person have certain health problems. Sickle cell anemia is one kind of anemia that is passed on through genes from parents to children in this way.

What Is Gene Therapy?
Gene therapy uses the technology of genetic engineering to cure or treat a disease caused by a faulty gene. This is a new kind of medicine, and scientists are still doing experiments to see if it works. One method they are trying is replacing faulty genes with normal, healthy ones. Gene therapy trials - where the research is tested on people - and other research may lead to new ways to treat or even prevent many diseases.

Updated and reviewed by: Robert Mason, PhD
Date reviewed: November 2001

Source: KidsHealth is a project of The Nemours Foundation which is dedicated to improving the health and spirit of children. Today, as part of its continuing mission, the Foundation supports the operation of a number of renowned children's health facilities throughout the nation, including the Alfred I. duPont Hospital for Children in Wilmington, Delaware, and the Nemours Children's Clinics throughout Florida. Visit The Nemours Foundation to find out more about them and its health facilities for children