Answer:
Meiosis.
Step-by-step explanation:
Meiosis is, by definition, "A special form of cell division in which each daughter cell receives half the amount of DNA as the parent cell", which is useful for mating and trait inheritance. For example, humans have haploid sperm and egg cells, which allows the resulting offspring to be diploid upon fusing of the two. Mitosis cannot be responsible for this, as in accord with what we know, DNA flows unidirectionally, with somatic cells not contributing to inheritance.
This could only mean that a mutation (e.g. Point, deletion, insertion, etc.) in the process of meiosis can cause changes in offspring phenotype.