During meiosis I, the chromosomes start pairing at (a) zygotene (b) pachytene (c) diplotene (d) leptotene.
Option A During zygotene or zygonema of meiotic prophase I the chromosomes become shorter and thicker. The homologous chromosomes come to lie sidebyside in pairs. This pairing of homologous chromosomes is known as synapsis, or syndesis. A pair of homologous chromosomes lying together is called a bivalent.
