Genetics is the study of genes—the units of heredity—and how the traits for which they carry coded information are transmitted from one generation to the next. Genes are found inside the cells of all living things. They get passed on from parents to offspring. Genes contain instructions for the production of proteins that determine how the body is made and how it functions. Some human traits that are controlled by genes include eye color, hair color, and height.

People have recognized for thousands of years that certain traits could be inherited. Early farmers crossbred animals and plants for desirable traits. Over many generations, they domesticated dogs and other farm animals from wild animals.

It wasn’t until the mid-1800s that people began to study the inheritance of traits as a science. A pioneer in these studies was Gregor Mendel, a monk living in what is now the Czech Republic. He performed a series of experiments with pea plants in the late 1850s. These experiments would lay the foundations of modern genetics. Mendel was the first to deduce that traits are determined by certain factors, too tiny to be observed. These factors come in pairs, one from each parent. Today we call these factors genes.

It took scientists several more decades to discover that genes are made of a complex molecule called deoxyribonucleic acid (DNA). DNA is constructed as a double helix—much like a twisted ladder. The hereditary instructions carried by genes are stored in coded form in DNA. Genes, which are located on structures called chromosomes, are segments of DNA.

Today, some scientists use genetic material from the DNA of extinct animals and plants to learn how those organisms evolved. National Geographic Society explorer Beth Shapiro, an evolutionary biologist at the University of California, Santa Cruz, extracts DNA from the remains of wooly mammoths, dodos, and other extinct animals. She wants to better understand the genetic changes that caused the demise of those animals. Other scientists may one day be able to use this information to help prevent modern-day animals from going extinct.