Here's why:

* Genes are segments of DNA that contain the instructions for building and maintaining an organism.

* Alleles are alternative forms of a gene. You inherit one allele from each parent, and these two alleles together determine the trait you express.

* Traits are the characteristics that are passed down from parents to offspring.

For example, the gene for eye color has multiple alleles. One allele might code for blue eyes, while another allele might code for brown eyes. The specific combination of alleles you inherit from your parents determines your eye color.