Here's a breakdown:
* Allele: A variation of a gene. For example, the gene for eye color can have a brown allele or a blue allele.
* Dominant allele: An allele that masks the expression of the recessive allele when they are paired together.
* Recessive allele: An allele whose trait is only expressed when two copies of it are present.
Example:
* Let's say "B" represents the brown eye allele and "b" represents the blue eye allele.
* A person with the genotype "BB" will have brown eyes because the dominant brown allele is expressed.
* A person with the genotype "Bb" will also have brown eyes because the dominant brown allele masks the blue allele.
* Only a person with the genotype "bb" will have blue eyes, as both alleles are recessive.
In essence, a dominant allele "wins" the competition for trait expression when paired with a recessive allele.
