Here's why:

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

* Alleles: Alleles are different versions of the same gene. You inherit one allele from your mother and one from your father.

* Variations: The specific combination of alleles you inherit determines many of your traits, like your eye color, hair color, and even your predisposition to certain diseases.

* Uniqueness: Because each individual inherits a unique combination of alleles from their parents, they are genetically unique.

Important Note: While alleles play a major role in our uniqueness, other factors also contribute, including:

* Environmental influences: The environment we grow up in can impact how our genes are expressed.

* Epigenetics: This is the study of how environmental factors can influence gene expression without changing the DNA sequence itself.

* Random chance: Even with identical genes, there's some randomness in how genes are expressed and how our bodies develop.

So, it's the interplay of alleles, environmental factors, and chance that makes each individual unique.