In a diploid individual, one chromosome carries A and B genes, and the homologous chromosome carries different forms (alleles) of these same genes, a and b. If there is a single crossover between these two genes involving non-sister chromatids during metaphase I of meiosis, the resulting four gametes are:

A. AB, AB, ab, ab.

B. AB, ab, AB, ab.

C. AaBb, AaBb, AaBb, AaBb.

D. AB, Ab, aB, ab.

E. Ab, Ab, aB, aB.