Genetics

Study of heredity and variation in living organisms.

Basic Concepts

Genes and DNA

What are Genes?

Genes are the instructions for building and operating all living things. These tiny segments of DNA hold the code that determines everything from the color of your eyes to how tall you might grow.

DNA: The Blueprint of Life

DNA (deoxyribonucleic acid) is a long, spiral-shaped molecule found in the nucleus of every cell. The structure of DNA is often described as a double helix, which looks like a twisted ladder. The rungs of this ladder are made up of four chemical bases: adenine (A), thymine (T), cytosine (C), and guanine (G).

  • A always pairs with T
  • C always pairs with G

Genes as Instruction Manuals

Each gene is a specific sequence of DNA bases that tells cells how to make a particular protein. Proteins do much of the work in your body, from building muscles to fighting infections.

Why Are Genes Important?

Genes are passed from parents to offspring, which is why you might have your mom’s curly hair or your dad’s dimples.

Fun Fact

Humans have about 20,000-25,000 genes!

How Do We Study Genes?

Scientists use special tools to read DNA sequences and identify genes, which allows them to understand how traits are inherited and how genetic diseases occur.

Examples

  • A gene for brown eyes is inherited from one or both parents, resulting in a child with brown eyes.

  • A mutation in a gene can cause cystic fibrosis, a genetic disorder.

In a Nutshell

Genes are sections of DNA that act as instructions for making proteins and determining traits.

Key Terms

DNA
A molecule that stores genetic information in all living organisms.
Gene
A segment of DNA that codes for a specific protein or trait.
Protein
A molecule made by cells, essential for structure and function in the body.