Final answer:
Mendel's law of independent assortment is a result of the way chromosomes line up and separate during meiosis, notably in metaphase I, and how genetic recombination can occur in crossing over during prophase I, with fertilization creating a zygote.
Step-by-step explanation:
The cellular process that underlies Mendel’s law of independent assortment is meiosis. During meiosis, specifically in metaphase I, chromosomes align randomly at the metaphase plate which allows for the independent separation of maternal and paternal chromosomes when the cell divides. This random assortment of chromosomes leads to genetic variation among the resulting gametes. Genetic recombination, which contributes to genetic diversity, can occur through the process of crossing over during prophase I of meiosis where sections of DNA are exchanged between homologous chromosomes. Finally, the zygote is the result of fertilization, a key step in sexual reproduction that restores the diploid number of chromosomes.