Final answer:
The principle in question is Mendel's law of segregation, which says that individuals have two alleles for each gene and each parent passes one allele to their offspring. This law explains why offspring inherit one allele for each trait from each parent and how dominant and recessive traits are expressed in the offspring's phenotype.
Step-by-step explanation:
The principle being described is known as Mendel's law of segregation, which is a cornerstone of genetics. This fundamental principle states that during the formation of gametes, which are the reproductive cells, alleles for each gene segregate from each other so that each gamete carries only one allele for each gene.
Thus, when an organism produces gametes, they contain just one of the two alleles for every trait present in the somatic cells. This means that if a parent has both a dominant and recessive allele for a specific trait, each offspring has an equal chance of inheriting either allele. When fertilization occurs, the resulting zygote will have one allele from each parent, leading to the restoration of the pair.
An individual who carries two different alleles for a gene, one dominant and one recessive (heterozygous), will express the dominant trait phenotype. Conversely, if an individual carries two identical alleles for a gene (homozygous), whether dominant or recessive, the corresponding trait will be expressed accordingly.