Here's why:

* Genes: These are the basic units of heredity, containing instructions for building and maintaining an organism.

* Alleles: These are different versions of a gene. For example, a gene for eye color might have an allele for blue eyes and an allele for brown eyes.

* Diploid organisms: Humans and most other organisms are diploid, meaning they have two copies of each chromosome. This is because they inherit one set of chromosomes from their mother and one set from their father.

* Inheritance: Each parent contributes one allele of each gene to their offspring.

So, when you get a gene from your parents, you get one allele from your mother and one allele from your father.