Final answer:
The distribution of genetic material in twins is correctly described by monozygotic and dizygotic distinctions, which refer to identical and fraternal twins, respectively.
Step-by-step explanation:
The distribution of genetic material between twins is described by whether they are monozygotic (identical) or dizygotic (fraternal), which is not listed in the mentioned options, but the concept is essential to understanding twin genetics. Codominance and incomplete dominance are types of genetic interactions, which are different concepts. For instance, if black and white true-breeding mice produce all gray offspring, this indicates incomplete dominance, where each parent's traits blend in the offspring.
In contrast, codominance would be demonstrated if both black and white colors appeared simultaneously in the offspring without blending, as seen in the ABO blood groups. Crossing over and independent assortment are mechanisms that contribute to genetic diversity, where crossing over refers to the process during meiosis when chromatids exchange segments of DNA, leading to genetic recombination, and independent assortment describes how different genes independently separate from one another when reproductive cells develop.