Here's a more detailed explanation:

* Genes are segments of DNA: They are like blueprints within our cells that contain the instructions for building and maintaining our bodies.

* They determine traits: These instructions dictate everything from our eye color and height to our susceptibility to certain diseases.

* They are passed down: We inherit half of our genes from our mother and half from our father.

* They can vary: Different versions of a gene, called alleles, can lead to variations in a trait. For example, there are alleles for blue eyes and brown eyes.

So, in short, genes are the fundamental units of heredity that carry the information necessary to build and maintain an organism.