So basically, the tetrid refers to the orientation of these individual four chromatids that are very close with respect to one another. Now, once synapses actually takes place and we form our chiasma, then crossing over actually takes place. So crossing over is a type of genetic recombination process in which we have the exchange of genetic information from this chromatid and this chromatid. So basically, crossing over produces two new recombinant chromosomes, as shown in the following diagram. So this section ends up on this chromatid, and this section ends up on or this section ends up on this chromatid to form the following two recombinant chromosomes. So crossing over produces our two recombinant chromosomes.