Mendel's law of segregation states that in a heterozygous individual, the two different alleles for a trait segregate equally during meiosis, leading to gametes with an equal likelihood of containing either allele. This results in a predicted 3:1 phenotypic ratio in the offspring when crossed with another heterozygous individual.
When applying Mendel's law of segregation to a person who is heterozygous for the gene that causes freckles, it means that this individual has inherited two different alleles for the freckle trait - one dominant allele (F), which causes freckles, and one recessive allele (f), which does not cause freckles.
During gamete formation, the alleles will segregate or separate so that each gamete carries only one allele for the freckle trait. As a result, there is an equal likelihood of this person producing gametes with either the dominant allele (F) or the recessive allele (f).
The principle behind this is that the two alleles for each gene segregate from each other during the process of meiosis. Thus, when this person has children, each child has an equal chance to inherit either allele. If we use a Punnett square to predict the offspring's possible genotypes, we will see that there is a 50% chance for the offspring to be heterozygous (Ff) if the other parent is also heterozygous for the trait.