The principle or law of heredity you're describing is called the Law of Dominance.

Here's a breakdown:

* Law of Dominance: This principle states that when an organism inherits two different alleles (versions of a gene) for a trait, one allele, called the dominant allele, will mask the expression of the other allele, called the recessive allele. This means that the organism will only display the trait associated with the dominant allele.

For example: If a plant inherits one allele for purple flowers (dominant) and one allele for white flowers (recessive), the plant will have purple flowers because the dominant allele masks the recessive allele.

Important Note: While the dominant trait is expressed, the recessive allele is still present in the organism's genetic makeup and can be passed on to future generations.