The recessive allele tends to (blank) when it's in the presence of the dominant allele.

The recessive allele tends to be masked when it's in the presence of the dominant allele.

Explanation:

Many of our traits are affected by our genes. From each of our parents, we receive one copy of every gene. These copies are called alleles.

There are different types of relationships that can occur between alleles. One of them is called dominance. This occurs when one allele masks the other, not allowing its effect to be expressed. The allele that masks the other is called the dominant allele (A), and the masked one is called the recessive allele (a). This means that an individual needs to have only one dominant allele in order for its effect to be expressed (AA or Aa). The effect of the recessive allele will be expressed only when an individual has both recessive alleles (aa).