Recombinations and variations in eukaryotic organisms are due to
The process of forming new allelic combination in offspring by exchanges between genetic materials of parents is called Recombination.
Variation is a change or slight difference in condition, amount, or level, typically within certain limits appear in the progeny compared with parents.
Recombination and variations appear in sexually reproducing organisms during meiosis and fertilization.
So, the correct option is ‘Meiosis and fertilization’.