When two parents (regardless of species) reproduce in sexual reproduction each offspring is generally a random combination of genetic traits from each parent. Their developed traits then depend on the expression of each of their genes per established genetic combinatory science. All well and good.
Now my question - when does the actual randomization of genes for a given offspring happen? Does it happen when the individual sperm and egg cells are formed, or does it happen when they combine?
So does every one of a female's eggs have the same genetics, and every one of a male's sperm have the same genetics, and when the two combine it is randomized to form the zygote?
Or is each egg unique and each sperm unique, and already "pre-randomized", and the combination to form the zygote is then a straight-forward addition?
Or is it some variation or combination of those two options? Maybe the answer actually even differs across species, or across plants vs animals, or fish vs mammals, or something?