When two or more forms of the gene for a single trait exist, some may be dominant while others are recessive.

Here's a breakdown:

* Dominant: A dominant allele expresses its trait even if only one copy is present.

* Recessive: A recessive allele only expresses its trait if two copies are present.

For example:

* Eye color: Brown eyes are dominant over blue eyes. Someone with one brown eye allele and one blue eye allele will have brown eyes.

* Hair texture: Curly hair is dominant over straight hair. Someone with one curly hair allele and one straight hair allele will have curly hair.

Let me know if you have any other questions!