Here's why:

* Alleles: These are alternative forms of a gene. For example, the gene for eye color might have a blue allele or a brown allele.

* Dominant Alleles: These alleles express their trait even if only one copy is present. They are typically represented with uppercase letters (e.g., B for brown eyes).

* Recessive Alleles: These alleles only express their trait if two copies are present. They are typically represented with lowercase letters (e.g., b for blue eyes).

Example:

* BB: Homozygous dominant (brown eyes)

* Bb: Heterozygous (brown eyes, because B is dominant)

* bb: Homozygous recessive (blue eyes)

So, when you see a lowercase letter in a genetic representation, it usually indicates a recessive allele.