Why do I have red hair? Why does everyone in my family have brown eyes? Why does my brother have freckles but I do not? A simple answer to these questions is genetics. Genetics is the study of how characteristics are passed from parents to offspring. All of the mentioned characteristics, or traits, are inherited. Inheritance is the passing of genetic information and traits from parents to their offspring. The study of genetics focuses on the information that is contained in deoxyribonucleic acid (DNA).

DNA is often called the genetic material of the cell. Genes are made of DNA. Each gene encodes for one protein. However, genes do not make proteins directly. DNA is located in the nucleus of cells, but protein synthesis occurs in the cytoplasm on structures called ribosomes. DNA contains all of the information for individual cell functions and processes.

DNA is a long, double-stranded molecule that is wound into a double helix. Each molecule of DNA is tightly wrapped around proteins. The DNA and proteins form structures called chromosomes. Humans have 23 pairs of different chromosomes, or 46 individual chromosomes, which are found in the nucleus of each cell. The DNA of each chromosome is composed of many genes. Approximately 2,000 different genes are found on each human chromosome. Each chromosome of a pair contains the same genes. The genes found on one pair of chromosomes are different from the genes found on another pair of chromosomes. That is, each pair of chromosomes contains different types of information. The information found on the chromosomes provides the instructions for cells to make different, individual protein molecules.

In order for scientists to study DNA, they must extract it from the nucleus of cells. Once extracted, the genes can be analyzed for genetic diseases and other characteristics. In Investigation One, students will extract DNA from the cells of onion using a procedure
combining techniques that scientists use for DNA extraction. Through this extraction, students will come to realize that DNA is found in the nucleus of cells. Students will also realize that one individual molecule of DNA cannot be seen by the naked eye or by a compound microscope from the lab. What students observe in the lab will actually be a cluster of many molecules of DNA from many cells that are extracted together.