The science of genetics isn't yet so advanced as to have a definitive answer to this, but there is a sound scientific theory as to when chiasmata (plural) are first seen.
A chiasma is a point where non-sister chromatids exchange genetic material.
It is thought that the exchange at chiasmata occurs during meiosis during the chromosomal crossover pachytene phase.
Then, the chiasmata first become visible, still during meiosis, during the diplotene stage of prophase I of meiosis. (Wikipedia)