Half of the gametes produced by an organism with the genotype Aa will receive the A allele, while half will receive the a allele. This is a demonstration of:

The correct answer will be segregation of alleles.

Explanation:

Gregor Mendel is known for his work on the pea plants bases on which he was able to predict the laws of inheritance.

His one of the observation was that during gamete formation or when the gametes form, the alleles get separated so that each gamete receives only one allele for each gene. He called this law as "Law of segregation" which shows that alleles segregate during gamete formation.

In the given question since alleles are separated this shows that example is demonstrating the segregation.

Thus, the segregation of alleles is the correct answer.