Genes, Chromosomes, and Inherited Traits

By the end of this lesson, you will be able to describe how genes inside chromosomes decide which traits an offspring inherits from its parents.

Almost every cell in your body holds a set of instructions for building and running that body. Those instructions are stored on chromosomes, which are tightly coiled threads of DNA found in the nucleus, the control center of the cell. Each chromosome is divided into thousands of smaller sections called genes, and each gene is a set of directions for making one part of an organism, such as a protein that gives hair its color.

A trait is any characteristic an organism has, like eye color, height, or the shape of a leaf. Traits that are passed from parents to offspring through genes are called inherited traits. When a mother cell makes egg or sperm cells, each one carries one copy of each chromosome. When an egg and sperm join, the new offspring gets one set of chromosomes from each parent, so it receives two copies of every gene.

Think about a litter of puppies on a Texas ranch. The puppies come from the same two parents, yet one may be black, one brown, and one spotted. That happens because each puppy received a different combination of genes from its mother and father. The genes for coat color were already sitting on the parents' chromosomes, and chance decided which copies each puppy got.

This is why offspring usually look similar to their parents but are never exactly the same. Genes create the variation you see in bluebonnets, longhorn cattle, and people, and that variation can help a population survive when conditions change.

Try it: If a calf inherits half of its chromosomes from its mother and half from its father, where did the genes for its horn shape come from?