Final answer:
The 13:3 phenotypic ratio is typically the result of a two-gene interaction involving epistasis, not caused by simpler patterns such as codominance, dominance at a single locus, or incomplete dominance.
Step-by-step explanation:
The question regarding the 13:3 ratio being produced is related to the field of genetics, specifically the inheritance patterns expressed as a result of different genetic interactions. This particular ratio is indicative of a two-gene interaction with epistasis, where one gene can interfere with or entirely mask the expression of another gene. No simple inheritance pattern such as codominant alleles, single-locus dominance, or incomplete dominance typically yields such a ratio. An example of epistasis is seen in the coat color of mice, where a gene responsible for pigment production can mask the effect of another gene responsible for the color type, leading to epistatic phenotypic ratios like 9:3:4.