And when the chromosomes intertwined, when they overlap onto one another, we have crossing over taking place. And what crossing over is it's the exchange of genetic information of chromosomal pieces among two noncystochromatids. So, remember, these two are cystochromatids with respect to one another. These two are cystochromatids with respect to one another. But this one here and this one here are noncystochromatids. That's because they are not identical to one another.