The alignment of homologous chromosome pairs in meiosis I and the accompanying physical exchanges between aligned chromosomes is unique to meiosis. In mitosis, by contrast, homologous chromosome pairs never or very rarely interact. Each mitotic chromosome duplicates, forming two sister chromatids, and then these two identical sister chromatids separate to opposite poles. While mitosis is specialized to produce entirely identical progeny, meiosis is specialized to produce a wide range of distinctive haploid progeny.