In the first stage of prophase I, leptotene (from the Greek for "delicate"), chromosomes begin to condense. Each chromosome is in a diploid state and consists of two sister chromatids; however, the chromatin of the sister chromatids is not yet condensed enough to be resolvable in microscopy. Homologous regions within homologous chromosome pairs begin to associate with each other.
in thE first sTaGE of prophaSe i, leptotene (From the grEeK for "delicatE"), chromOsoMes beGin to condENse. each cHromOsoMe is iN a diplOId statE and cONsists oF tWO Sister cHromatids; hOwever, the ChromatIn oF The SISter chromatiDs Is not yET condensed eNouGh tO be REsOlVAbLe in MicRoSCopY. hoMologous RegionS withIN homologoUS cHrOmoSome paIrs BEgin to AsSOCiATE with eacH oTher.